I had the pleasure today of beating my head against the wall trying to find a workaround for a known bug in IE6. The problem shows up when you try to using a floating element via the commonly used CSS float: right command, for example. Apparently IE6 will often expand the float element to 100% width before placing it, which sort of defeats the purpose of asking for it to float.
I couldn't find a work-around for my case that still worked in Firefox and IE7.
Well, hopefully Firefox will continue to gain popularity and eventually IE will die a slow death.
I've tried IE7 and don't really like the interface changes at all. Long live Firefox.