I have a computer that I use for surfing with a microsoft OS that I errhm got really cheap off the intertubes and it won't let me upgrade to ie7 because of it. Guess you don't want me as a customer. Along with the roughly 30 million people with money in their wallets that have the same problem.
What I'm saying is that if 30% of the users who go to your site (the number is grabbed out of thin air btw.) use IE6 then your site should deal with it. Everything else is like stopping 30% of your customers at the door telling them that they can't spend their money here and will have to go over to you competitor.
