That question drew a lot of response. This section is one of the most popular. It is right up there with Regular Expressions. So I decided to revisit the topic.
IE 7 now supports :hover on all HTML element
The examples now use conditional comments (see Journal entry on conditional comments) to separate IE code. Originally, the code depended on browsers ignoring IE's proprietary features. Using conditional comments separates IE 6 from IE7 and pages more easily validate.