Some work, not all
Wonder what PS3 games will work with the PS4's Dualshock 4 controller? Reddit has a good list going already. It looks like most of the games tried so far, though some do nothing, including some big titles like Gran Turismo 5 and Grand Theft Auto V. As we've heard before, not everything works.
Note that if the PS3 game requires motion sensing, you're out of luck. Also, you'll have to play with the USB cable connected to your PS3. Both are bummers, but at least we have something to do with these early Dualshock 4 controllers for these weeks leading up to launch.