A bit of the old, a bit of the new regarding this topic...
While I think all of us agree that when we provide our services to our clients, we should make their sites IE6-compatible, that same sort of professional responsibility isn't necessarily passed on to ourselves.
Point is: If we own the site, we have the right/option to simply drop IE6 support, and inform the visitor that a) they are using a browser that is most probably older than their pet, b) that they are exposing themselves to a host of security problems, and that c) their browser is preventing them from experiencing some modern technology *ahem*, and that they will only be experiencing a small taste of what the website has to offer *ahem*.
The reason I say this is: if we, as site owners, start making the effort to gently prod/push/encourage casual visitors, little by little, people would be inclined to upgrade/download and install Opera/Firefox. After about a year of two (ok, maybe about half a decade) of this kind of gentle prodding, we may just see IE6's numbers in the lower 10's of the browser percentages.
What do you think?