I too have had issues with PD 10. The first is that I couldn't set up my Windows XP VM with anything more than 2 gigs of memory, anything more and the VM would hang (upgraded from 9 to 10). I worked with Parallels support on this, submitted problem reports, maybe there will be a fix in a future version. Until then my XP VM is limited to 2 gigs.
Then I had problems with Microsoft Flight Simulator 2004, it now won't run in coherence mode, won't even run in full screen. In coherence it just comes up with a black screen, no display of the cockpit. I can access the menu, but never get anything displayed. In full screen, if I move the mouse the screen goes bonkers.
So I gave up and downgraded to PD 9, but my problem with running FlightSim in coherence or full screen is still there, can't figure out why. I deinstalled Parallels tools, removed Parallels 10 using AppCleaner, then installed PD 9, guess there is still something somewhere on the MAC or in my pvm file that is hosed. So it goes...
Ian