Lets take that a step further and say that they will always be BEST on a PC, with a fully customizable keyboard and mouse.
Thing that really bothered me about the PSP is the single analog nub. I am avid FPS fan and the PSP would do wonders with another nub.
Yes Vega, you do have legitimate concerns, but the only reason we really need the face buttons on the PSP is because we DONT have a second analog nub to put aim/strafe on. With two nubs we could have one nub for forward/backward/left/right movement, another for up/down/left/right aiming and that leaves us the shoulder buttons for Fire, Jump, Use, etc. The face buttons would be relegated to actions that are used less, like reload, switch weapon, switch item (if inventory is present).
All in all, a second nub will greatly improve the PSP's ability to play FPS games.