All posts must have a main category. When writing a new post, it starts out as a member of the default category. You can then change it, as well as marking extra categories.

OK. So the default category selects the default category that a new post is place into. I has nothing to do with how they are displayed. Thanks for that info. That answers my first question. Thanks again for taking the time to reply.

The 2nd question definately sounds like it would be a system enhancement. I will continue to poke around at the code for a hack. Any hints or tips as to where to look would be appreciated.

So you have a bunch of posts in other categories that you don't want to show on the main page...?

Exactly.
That would provide the ability to organize and decrease clutter.
For example a category may be "Event Highlights". That category would allow posts to be shared which are somewhat off topic that you wouldn't necessarily want to clutter the main page with. Someone interested in the event would have a concise location to go for that information without cluttering the main page.

Could you use a sidebar link to do that instead of a post defined by category?

To do a sidebar page, in the back office goto posts/comments, move to the "sidebar links" tab, and then click the "new link" hyperlink.

To be honest, I'm not sure. I looked through the online documentation and tried making some changes in the backoffice. I really couldn't tell what the sidebar links do.
It didn't seem to do what you suggest. ??