I have had a lovely week trying to rebuild/recover my SharePoint 2010 staging environment. I applied the August 2012 Cumulative Update.
The last thing to get working was the user profiles. And of course…it got stuck on starting. There wasn’t much to go on and I tried all of the usual techniques to get it to work.
I decided to backup my production Profile DB, Sync DB and Social DB and restore them to Staging.
Eventually to cut a long story short, I deleted the User Profile Service and deleted the Sync DB. Then I recreated the UPS using the remaining Social DB and Profile DB.
After doing that, the User Profile Synchronization service started okay.