I really wish there were more blog posts like this one, it covers a whole host of problems IE has with CSS, from the lack of :hover support, to the well known issues with PNG files - oh and check out the comments, an awful lot of clever people have replied with other issues / fixes for issues with IE - oh and some stuff on CSS3 Media Queries - which seem just incredibly useful - anyone know when / if IE will support CSS 3?
I also discovered this as a link from that article, essentially it's a nice, simple, standards compliant (for which read, accessible, lightweight and cross-browser compliant) drop-down menu system - it's also the only menu system I've seen which is just phenomenally easy to do in an ASP.NET repeater - which is VERY handy - look out for a new menu soon on this site :-)!