I think officially, 4% of users still use IE 7. [Edit: Source: http://theie7countdown.com/] Back in the day, IE was the most popular browser on the Internet, and I'm sure there are a lot of corporate applications written specifically for its quirks that simply don't work in newer browsers. Heck, the University of Waterloo's Learning Management System (based on the open-source Angel LMS) was broken in Chrome for the longest time -- the solution was to migrate to a different (closed-source) product altogether.
