I got stuck in this same problem earlier today. I tried build clean on my project and started getting the "c1xx : fatal error C1083: Cannot open source file: 'Release\moc_xxxx.cpp': No such file or directory" errors.
After much frustration with vs2010, I figured two things out:
I could get the moc_xxxx.cpp files to come back using the "Restore previous versions" options that came with my version of Windows. Every time you update windows, it takes a snapshot of your recently changed files and saves it on your harddrive.
After getting it to that point, I also found another "fix" but this is more of a hack than a fix. For every .h file that you want to force Moc'ing for, (so any of them with a Q_OBJECT macro in them) you can tell visual studio to explicitly build the .h file (right click on the file and choose compile, or press Ctrl-F7 while in the .h file).
Then the next time you build, it can find the Moc'ed file and the error goes away.
I hope that helps someone.
It would be nice if there was an option built into the Qt menu on the VS plug-in that could do that for you (such as "Regenerate All Moc Files") or if it could notice that the moc files don't exist and built them so that you can recover after a build clean.