There are quite a lot of companies that have applications that rely on IE6. I, personally, know of a few financial institutions that can't update. This might not be necessarily related to their systems not being able to work with a newer version, though. Some office drones are just incapable of doing there job if the color of a button changes. I kid you not.

Other companies have a long(!) cycle when evaluating new software releases. I have heard of an insurance provider that rolled out IE7 just this year.