[Edit: Life is getting much better these days with IE 9 beginning to support standards and be consistent as Firefox and Safari (and now Chrome and there is always someone on Opera)]
Usually, I start out creating my designs for this site by testing them in Safari (yes, I am a Mac user… so consider this my first contribution to the holy war of mac vs pc). I also test Mozilla on the Mac/Windows and feel that if it looks good in those two I am generally on track. Eventually, I get around to checking in IE on Windows and then IE on the Mac (although, I don’t know why anyone would still use IE on a Mac). Here, I typically find some fatal flaw that IE just craps on. If it were not for the fact that Windows forces users to use IE (software update with Moz, I don’t think so), most everybody would have chucked it a long time ago. Now, only due to the security lapses in IE, has Firefox (Mozilla’s light and fast version) begun to claim some users back from IE… but you still have to use IE. And most users still do…