Have been happily using the UXStyleCore service for a long time to allow for custom theming in Windows 7 without having to patch files.
And then, I applied the Windows 7 SP1 update ...
Don't know exactly what it did, but when I restarted, the theming was gone and the service was gone, too.
To solve it, did the following:
1) Downloaded fresh copy of the UXStyleCore SW
2) Set UAC to lowest level
3) Rebooted PC
4) Installed the UxStyleCore app again
5) logged off and back on
6) Redid the aero.msstyles file swapping
Got the theming back OK now.
BTW, am running Win 7 Basic because this chipset does not support Aero. Don't know if those of you running Aero themes will run into the same problem.