It's sad some people here doesn't seem to understand why IE6 is still used to this day.
Like a few have already pointed out, it's a matter of money.
Because IE6 is the only Microsoft browser still working under Windows 2000, which was the successor of Windows NT, which was the only viable alternative for professionnal network back in 2000.
Lots of entreprises, mainly public ones, which still use Windows 2000, can't get anything new thanks to Microsoft for keeping new versions to newer Windows (Office 2007 isn't supported under Windows 2000).
When you have hundreds of computers, with dozens of critical applications specifically written for this environnement, you won't throw everything out the window to keep up the pace.
Not only it will drain massive amount of money, but you will be unenable to work efficiently during the process.
It's a several years planning we're speaking of.
With lots of uncertainties along...
And of course, it is even more out of the question for less wealthy compagnies or countries.
Did you know that typing a document in a wordprocessor is still a luxury in some regions of Africa?
And Microsoft wants to force all those people who make barely enough to eat, to invest into a brand new system worthy of a whole life salary?
All those people would be happy to use IE9 or Firefox 4 or Google Chrome.
Problem is, either those are unavailable for their old system (Windows 2000 or earlier), or they run too slowly to be efficient.
And don't tell them to go Ubuntu, Windows 2000 is still faster on a older rig (P4, 256 MB).
Half the world hasn't the funding to please Microsoft.
Sadly he doesn't give a sh*t...