Re Standards support, there are a few things which I've found frustrating about IE (various versions), like the lack of support for transparency in PNGs without a horrible hack (AlphaImageLoader), and various CSS problems - here's a few:

http://www.quirksmode.org/css/contents.html

I wouldn't call that the best support, it's not bad, but there are better browsers, and Microsoft doesn't seem inclined to fix it before 2007. According to that table, it doesn't seem to be the most complete implementation at all (of CSS). The XSLT support is very nice, I wish other browsers had that.