i have an addon that posts a warning to anyone using IE6 that they need to upgrade, and have banners stating the site works best with firefox.
I had so many people griping over problems, they all switched to FF and are happy as clams now.
"No matter where you go, there you are."
"If you can't do something smart, Do something right"
"There are three kinds of people in the world, those who can count, and those who can't"