I use Gameboid (Gameboy Emulator) and Snesoid (SNES Emulator) without any problems. The trackball works as a DPAD. For games like Mario, tilting the screen to move also works. You can map game buttons to Volume Up, Down, Search, back, and Call. No problem with any games so far. The hard buttons are more responsive that the Search and Back buttons which are both touch. There is also an on screen d pad and on screen touch Start and Select buttons that you can toggle on or off.
So far all of the games in the market that I have tried work for me. Jewels, Bonsai Blast, etc are all designed for touch screens