You can set each post to have it's comments disabled when you post. I know you can do this for all posts, but I'll have to look at which file to edit.

0.9.1: One of the peeps who writes a blog I maintain asked the same of me this morning. I opened main.php in the default skin she uses and changed:

$disp_comment_form = 1;

to

$disp_comment_form = 0;

She only uses one skin, so that should stop the comment form from displaying. I've no idea if this will work against spambots. I suppose I'll find out soon though.

Phoenix Alpha: There's a setting in the blogs tab to turn off all trackback, pingback, and comments for a given blog. It's a sweet little feature.