With the help of JibbaJabba, I recently got a PSP, and got it up and running with various emulators. I thought I remember people saying that the SNES emulation was pretty bad.
I've been using snes9xTYL-0.2c emulator, and it seems to be pretty damn good. You have to run the cpu at 333mhz, and you have to do 1 or 2 frameskips, but other than that, and the fact that the soundtracks aren't reproduced entirely correctly, I would say it's damn good, all things considered.
I was playing Castlevania 4 on it, and it seemed to be working just fine. It's not perfect by any means, but it's definitely very playable. I thought I remember people saying that SNES emulation on the PSP still isn't a very viable option yet? I think the take was that some SNES games could run pretty good, but the vast majority were totally unplayable, and that trying to play SNES games on the PSP was pretty much a waste of time.