MAME to hit iPhone

I'm sure there are a lot of you who have never heard of MAME, but I'm sure that all of you have heard of the iPhone. MAME stands for Multiple Arcade Machine Emulator, and the one for the iPhone is based on the SDL version of the emulator meant for the Ubuntu Linux platform.
I have heard that the performance is not equal to the classic stand up games. Simple games like Pac-man or Q-Bert (not pictured above, the one on the right is Burger Time) can run at normal speeds, but more complex games will cause trouble.
What I want to know is: how you play these games on a touchscreen?
Via Coolest Gadgets