:hover does only work on links (<a> tag) on Internet Explorer !
If you want to implement a “Pure CSS Menus” and for that using <ul> and <li> tags and if you rely on :hover applied to list items, not links, it will perfectly work on non-IE browser ! If you use IE browser, than you can call Houston ! You have a problem !
You will also find a rather long article on all the “Side-stepping IE” on Mezzoblue
That hack and some others will be used in the next release of this site to have the same behaviour while browsing on all browsers (standard compliant or not….! ;p
Not yet ready to move your browser to a compliant browser ? lol 😉