I am starting to come to the conclusion that all the downsides of not supporting IE6 are for the most part mythological (particularly outside of corporate intranet situations like you identify).

I mean, if you "don't support" IE6, what is the worst thing that happens? Some stuff doesn't look right for a portion of your audience? These people already have a seriously degraded internet experience, are they going to notice that the padding on your floats is all messed up?

I am pretty certain that you are leaving revenue on the table if you choose to ignore IE6 as a business, which is a valid objection to my argument. But how much?

And how much costs are you leaving off the table by freeing your designers and developers from supporting IE6, and allowing them to do other amazing things with their precious time?

Give me two almost-identical websites with two similar, business-oriented audiences, then have one site support IE6 and the other basically ignore it (and use the excess development/design time to build other features). I don't know about you, but I'd put my money in #2.