The SuperNES emulator for iPad is extremely fast and, according to Snes4iphone developer ZodTTD, "it looks, sounds, and plays great." The best thing: It's just a quick port of the iPhone version. The worst thing: It's not an official app.
I just got my iPad and the first thing I did was install a build of snes4iphone made specifically for non-jailbroken iDevices. This is the video of the first test. I have 2x scale enabled on the iPad to make it full screen, and I enabled smooth scaling in the emulator. I'm playing Super Mario Kart on my iPad and it looks, sounds, and plays great! This is going to be amazing.
The scaling is going to be needed in any case for all these emulators, since their maximum resolution matches the iPhone. The iPad screen resolution is comparatively huge. Also, I hope he implements new controls, similar to those of Geometry Wars.
I wish Nintendo could stop with the snubbing and realize that they may have a huge business opportunity by selling their old stuff in an official NES/SNES/N64 emulator with its own storefront. [Techtosh]