Tried hack to force 4.2 update, result is a broken play store. Theories? So I'm on a Galaxy Nexus.  Still on 4.1.  I tried the 'hack' where you clear data on the Google Services Framework, then check update, but no luck.  I shrugged and got on with my day.

Now I'm noticing that I have several updates in the play store.  And if I choose "update" all I get is an instant "Update for [app name] could not be downloaded".  Repeatedly.

I've tried clearing data for the play store, rebooting, but nothing.

Yay. Any theories?
Remove and add again your Google (main) user account. This should do the trick.