How about when you upgraded to IE7?
Try Firefox 2.0.2?
IE7 has a few quirks that are causing problems with other sites I visit. All my other machines that are running IE6 seem to run better for the same pages.
Same with Firefox. 2.0.2 was running great as was 1.5.x but for some reason 2.0.3 keeps crashing.. On the forum as well as a few other sites. I'm doing some more testing and sending reports back to Mozilla. I'll start playing with ie7 to see what is going on. You might try changing your settings back to simple text editing for your message composing rather than the full WYSIWYG or switching to WYSIWYG rather than simple or advanced text to see if one works better. It might be the WYSIWYG plugin that is causing some of the problem.