Anyway seeing 1.8 just got released, here are the modifications that let you have grouping for your plugins.

Firstly here is a screenshot;
http://blogs.balupton.com/plugins/plugin_grouping_v1.0.0.0.gif

And heres the modifications;

[ File: /blogs/inc/_misc/_plugins.class.php ]

Add the following anywhere inside the Plugins Class:

   /**
    * Will return an array that contents are references to plugins that have the same group, regardless of the sub_group.
    */
   function get_Plugins_in_group ( $group ) {
      $result = array();
      
      foreach( $this->sorted_IDs as $plugin_ID )
      {
         $Plugin = & $this->get_by_ID( $plugin_ID );
         if( $Plugin->group == $group )
            $result[] = & $Plugin;            
      }
      
      return $result;      
      
   }
   
   /**
    * Will return an array that contents are references to plugins that have the same group and sub_group.
    */
   function get_Plugins_in_sub_group ( $group, $sub_group = '' ) {
      $result = array();
      
      foreach( $this->sorted_IDs as $plugin_ID )
      {
         $Plugin = & $this->get_by_ID( $plugin_ID );
         if( $Plugin->group == $group && $Plugin->sub_group == $sub_group )
            $result[] = & $Plugin;            
      }
      
      return $result;      
   }


   /**
    * Callback function to sort plugins by group.
    *
    * WARNING: do NOT sort by anything else than priority unless you're handling a list of NOT-YET-INSTALLED plugins
    */
   function sort_Plugin_group( & $a_ID, & $b_ID )
   {
   
      $a_Plugin = & $this->get_by_ID( $a_ID );
      $b_Plugin = & $this->get_by_ID( $b_ID );
      
      // Compare Group
      $r = strcasecmp( $a_Plugin->group, $b_Plugin->group );
      if( $r != 0 )
         return $r;
      else {
         // Compare Sub Group
         $r = strcasecmp( $a_Plugin->sub_group, $b_Plugin->sub_group );
         if( $r != 0 )
            return $r;
         else {
            // Compare Name
            return strcasecmp( $a_Plugin->name, $b_Plugin->name );
         }
      }
               
   }

Add the following to the switch statement inside the sort() function inside Plugins Class:

			case 'group':
				usort( $this->sorted_IDs, array( & $this, 'sort_Plugin_group') );
				break;

So you should end up having something that looks like:

	/**
	 * Sort the list of {@link $Plugins}.
	 *
	 * WARNING: do NOT sort by anything else than priority unless you're handling a list of NOT-YET-INSTALLED plugins!
	 *
	 * @param string Order: 'priority' (default), 'name'
	 */
	function sort( $order = 'priority' )
	{
		$this->load_plugins_table();

		foreach( $this->sorted_IDs as $plugin_ID )
		{ // Instantiate every plugin, so invalid ones do not get unregistered during sorting (crashes PHP, because $sorted_IDs gets changed etc)
			$this->get_by_ID( $plugin_ID );
		}

		switch( $order )
		{
			case 'name':
				usort( $this->sorted_IDs, array( & $this, 'sort_Plugin_name') );
				break;
				
			case 'group':
				usort( $this->sorted_IDs, array( & $this, 'sort_Plugin_group') );
				break;
				
			default:
				// Sort array by priority:
				usort( $this->sorted_IDs, array( & $this, 'sort_Plugin_priority') );
		}
	}

[ File: /blogs/inc/_misc/_plugin.class.php ]

Add the following before the constructor "function Panel()":

	/**
	* Grouping
	*/
	var $group = '';
	var $sub_group = '';

[ File: /blogs/inc/VIEW/_menutop.php ]

Look for the following around line 80:

	global $Debuglog;
	$Debuglog->add( 'Admin-Path: '.var_export($this->path, true) ); 

And replace with:

	global $Debuglog;
	$Debuglog->add( 'Admin-Path: '.var_export($this->path, true) );
			
	if( $GLOBALS['ctrl'] == 'plugins' ) {
		?>
	<style type="text/css">
	table.grouped tr.PluginsGroup,
	table.grouped tr.PluginsSubGroup {
		text-align:left;
	}
	table.grouped tr.PluginsGroup th,
	table.grouped tr.PluginsSubGroup th {
		border-left:none;
	}
	
	table.grouped tr.PluginsSeperator th {
		height:7px;
		background-color: #f5f3ef;
		border-top: 1px solid #9e9286;
	}
	table.grouped tr.PluginsSubGroup th {
		border-bottom: 1px solid #9e9286;
		border-top: 1px solid #9e9286;
	}
	
	table.grouped tr.PluginsSubGroup th {
		background-color: #efede0;
		color:#666666;
	}
	table.grouped tr.PluginsSubGroup th,
	table.grouped tr.PluginsSubGroup td.firstcol {
		padding-left:15px;
	}
	</style>
		<?php
	}

[ File: /blogs/inc/VIEW/settings/_set_plugins.form.php ]

Look for the following around line 80:

		<?php
		$apply_rendering_values = $admin_Plugins->get_apply_rendering_values(true); // with descs

		$admin_Plugins->restart();	 // make sure iterator is at start position
		$count = 0;
		while( $loop_Plugin = & $admin_Plugins->get_next() )
		{
		?>
		<tr class="<?php echo (($count++ % 2) ? 'odd' : 'even') ?>">

And replace with:

		<?php
		$apply_rendering_values = $admin_Plugins->get_apply_rendering_values(true); // with descs

		// Sort the plugins by group
		$admin_Plugins->sort('group');
		// Grouping
		$current_group = false; // False so it does the header once
		$current_sub_group = '';

		$admin_Plugins->restart();	 // make sure iterator is at start position
		$count = 0;
		while( $loop_Plugin = & $admin_Plugins->get_next() )
		{
		
			if( $loop_Plugin->group !== $current_group ) { // Reason why $current_group is false
				$current_group = $loop_Plugin->group;
				$current_sub_group = '';
				$count = 0;
				?>
				<tr class="PluginsSeperator">
					<th colspan="8"></th>
				</tr>
				<tr class="PluginsGroup">
					<th colspan="8"><?php
					echo T_(
						( $current_group == '' || $current_group == 'Un-Grouped' ) ? 'Un-Grouped' : $current_group
					); ?></th>
				</tr>
				<?php
			}
			
			if( $loop_Plugin->sub_group != $current_sub_group ) {
				$current_sub_group = $loop_Plugin->sub_group;
				$count = 0;
				?>
				<tr class="PluginsSubGroup">
					<th colspan="8"><?php echo T_( $current_sub_group ); ?></th>
				</tr>
				<?php
			}
		
		?>
		<tr class="<?php echo (($count++ % 2) ? 'odd' : 'even'); if ( $current_sub_group != '' ) echo ' PluginsSubGroup'; else echo ' PluginsGroup'; ?>">

Now look for the following around line 188:

		</tr>
		<?php
		}
		?>
		</tbody>
	</table>
	<p class="center">
		<a href="admin.php?ctrl=plugins&amp;action=reload_plugins"><?php echo T_('Reload events and codes for installed plugins.') ?></a>
	</p>
</fieldset>

And replace with:

		</tr>
		<?php
		}
		// Sort the plugins by name again
		$admin_Plugins->sort('name');
		?>
		</tbody>
	</table>
	<p class="center">
		<a href="admin.php?ctrl=plugins&amp;action=reload_plugins"><?php echo T_('Reload events and codes for installed plugins.') ?></a>
	</p>
</fieldset>

Now find the following around line 210:

if( empty($AvailablePlugins) || ! is_a( $AvailablePlugins, 'Plugins_no_DB' ) ) // may have been instantiated for action='info'
{
	// Discover available plugins:
	$AvailablePlugins = & new Plugins_no_DB(); // do not load registered plugins/events from DB
	$AvailablePlugins->discover();
	$AvailablePlugins->sort('name');
}
?>

And replace with:

if( empty($AvailablePlugins) || ! is_a( $AvailablePlugins, 'Plugins_no_DB' ) ) // may have been instantiated for action='info'
{
	// Discover available plugins:
	$AvailablePlugins = & new Plugins_no_DB(); // do not load registered plugins/events from DB
	$AvailablePlugins->discover();
	// $AvailablePlugins->sort('name'); - Not needed as we sort by group in the next line
}

// Sort the plugins by group
$AvailablePlugins->sort('group');
?>

Now find the following around line 238:

		<?php
		$AvailablePlugins->restart();	 // make sure iterator is at start position
		$count = 0;
		while( $loop_Plugin = & $AvailablePlugins->get_next() )
		{
		?>
		<tr class="<?php echo (($count++ % 2) ? 'odd' : 'even') ?>">

And replace with:

		<?php
		// Grouping
		$current_group = false; // False so it does the header at least once
		$current_sub_group = '';
		//
		$AvailablePlugins->restart();	 // make sure iterator is at start position
		$count = 0;
		while( $loop_Plugin = & $AvailablePlugins->get_next() )
		{
		
			if( $loop_Plugin->group !== $current_group ) { // Reason why $current_group is false
				$current_group = $loop_Plugin->group;
				$current_sub_group = '';
				$count = 0;
				?>
				<tr class="PluginsSeperator">
					<th colspan="5"></th>
				</tr>
				<tr class="PluginsGroup">
					<th colspan="5"><?php
					echo T_(
						( $current_group == '' || $current_group == 'Un-Grouped' ) ? 'Un-Grouped' : $current_group
					); ?></th>
				</tr>
				<?php
			}
			
			if( $loop_Plugin->sub_group != $current_sub_group ) {
				$current_sub_group = $loop_Plugin->sub_group;
				$count = 0;
				?>
				<tr class="PluginsSubGroup">
					<th colspan="5"><?php echo T_( $current_sub_group ); ?></th>
				</tr>
				<?php
			}
		
		?>
		<tr class="<?php echo (($count++ % 2) ? 'odd' : 'even'); if ( $current_sub_group != '' ) echo ' PluginsSubGroup'; else echo ' PluginsGroup'; ?>">

Then find the following around line 307:

			</td>
		</tr>
		<?php
		flush();
		}
		?>
		</tbody>
	</table>
</fieldset>

And replace with:

			</td>
		</tr>
		<?php
		flush();
		}
		// Sort the AvaliablePlugins by Name again
		$AvailablePlugins->sort('name');
		?>
		</tbody>
	</table>
</fieldset>

To add grouping to your plugins just add the variables; $group, and $sub_group, to your plugin appropriatly.

Enjoy.