Its been 10 years since Internet Explorer 6 was launched, think how many different ways you use the internet now compared to 10 years ago? To the different experiences we expect from web sites. Then ask why are you still using a product so out of date when its free to upgrade?
Microsoft have started a countdown page to get the amount of users of IE6 down to under 1% its currently 12% worldwide, and 3.5% in the UK.
Its an interesting site and gives links to get up to date.