CSS3pie Module Works Fine
Some people like the rounded corners that CSS3 can give to things like blocks and menu tabs. The problem has been that Internet Explorer doesn't support that while Firefox, and Google Chrome do.
CSS3PIE was created to solve this and other issues in IE, and Drupal has a module for that by the same name CSS3pie. I have it working here at PcHousekeeping.com after a little fiddling. The only real edit I had to do was to add position:relative to the two selectors that give the main menu tabs rounded corners.