This log file no longer exists in Windows 7 / Windows 8 and Microsoft has moved majority of the Group Policy logging to the new "Applications and Services Logs" under Group Policy\Operational. The only caveat however from my experience is these logs are no where near as verbose as the logs provided under the legacy Userenv.log.
You can however enable verbose logging on Windows 7 / Windows 8 computers by adding an additional registry key, this procedure however has not been documented officially by Microsoft on TechNet and should be used for advanced troubleshooting only as a last resort.
The registry key which turns on advanced verbose logging is as follows.
The resulting log file “gpsvc.log” can be found %WINDIR%\debug\usermode.
Hope this post assists you in whatever group policy troubleshooting your currently performing!