Microsoft has not done anything to stop the Windows 7 activation crack because it is still active and running all around. Even when Windows 7 final was not out and was in testing mode, pirates were able to crack Windows 7. Out of curiosity I have tested couple of these which are working and by using these you can crack Windows 7 permanently.
There has been a lot of trend lately to use custom themes for operating system to transform it into another. For example you can use Windows XP with a custom Windows 7 theme. In this case your Windows XP will completely look like Windows 7. Now some of users will not be able to run such modifications or transformations for their XP if its XP sp2 or sp3 (with Microsoft Service Pack updates). In this case they will have to allow third party themes for Windows.