IE6 is the devil: we all know it. Especially when you get to design your own theme and have to do IE6 bug fixing for hours after you actually finished to code for all other browsers.
Luckily, Nathan Rice gives us here a great solution: Serve IE6 users the default WordPress theme. Thus you don’t have to worry about bug fixing anymore!
For skepticals, I advise you go have a look at the code he published in this tutorial: there are other potential uses for this tutorial!