Since IE6 did a shit job of complying with web standards, there are many companies running around with older corporate software that only works on IE6. Updating that old software in this economic climate, would be pretty burdensome.
Updating to IE8 destorys the IE6 installation, and methods to get both browsers installed at the same time are iffy at best. So... for a modern browser, the best solution is to install something like Firefox, Chrome, or even Opera. These adds will probably hurt Microsoft.
That's what they get for integrating the browser into the OS the way they did. Looks like its finally catching up with them.