The rule of the thumb regarding backwards compatibility is to support all major browsers 1 version behind and drop support for browsers that are under 5% in global use. as you can see from the tables in the bellow posted link IE6 was in 27.26% in december 08
You simply can't ignore over a quoter of the users out there simply because its too much trouble to support that browser. When it comes down to it we as developer need to provide the best user experience for all users and until those users decide that IE6 is bad and they move to IE 7 or FF we can not stop supporting it. Its just one of our duties as developers.