I guess it depends on your audience. If you website is a general public site, then you should strive to support IE6 as best you can.
One of our websites, which gets monthly uniques in the millions range shows the following browser stats:
Browser
Visits
% visits
Internet Explorer
x,xxx,xxx 67.56%
Firefox
3xx,xxx 21.10%
Safari
xxx,xxx 8.67%
Chrome
xx,xxx 1.65%
Mozilla
x,xxx 0.37%
Out of which Internet Explorer accounts for:
Browser Version
Visits
Browser Version contribution to total:
1.
7.0
xxx,xxx 60.19%
2.
6.0
3xx,xxx 26.00%
3.
8.0
1xx,xxx 13.78%
So, for this specific website, IE6 still beats Firefox by a slim margin IE6 is very close to Firefox in regards to total number of visitors, so it needs to be supported.
I would be curious to see StackOverflow's browser stats. I believe that if your visitors are more technical, you'll likely see much smaller numbers of IE6 visitors (or any IE version for that matter).