According to the Forrester report, Updated 2010: Windows 7 Commercial Adoption Outlook, Windows 7 "powers one out of every 10 PCs within North American and European companies." Windows XP, the report says, powers 75%.
A lot of that, of course, is due to installed base --- Windows XP has been around since 2001, and it's a stable operating system, so enterprises that have adopted it tend to stay with it. Windows 7 has only been around a year.
But even on new PCs, enterprises still shy away from Windows 7, with IT managers deploying it on only 31% of new PCs. That will change, however. The report says that within a year, 83% of new PCs going into businesses will run Windows 7.
So even though the numbers for Windows 7 in the enterprise aren't impressive today, they will be in the future, and by that time the debacle of Windows Vista in enterprises will be long forgotten.