It’s 74%, in fact, according to this endgadget.com story. Based on my own experience I would add that IT expense and software compatibility are the two keys. Even though I’ve found that most software issues can be resolved without excessive effort, I did run into one case in which Quicken Home Inventory would not run on Windows 7, and it turns out it really won’t. Nonetheless I still have a number of Windows XP computers running in client offices.
The only surprise here for me is that Microsoft® is going with the flow rather than trying to force the new operating systems on everyone. I think they’re wise. Over time, people will upgrade, especially as they buy new hardware, and so the new gets to beat the old.