I think I might stick with the snes or gameboy emulators, unles grpjic chip support is implimented, od froyo really speeds things up a lot.
As it is, things can run, but because of control issues (not using the original controller), or slow speed issues, I've yet to see a game thats really "fun" to play.
The app is impressive that things actually run on a smartphone, and usually emulators improve speed wise over time, so it really depends if the developer actually sticks with it and optimises it.
I'd really love to see a good MAME emulator before n64 myself... old arcade games are small, so they don't use much storage space, and they are perfect for on the go quick gameplay. Plus they aren't cpu intensive compared to the newer game systems, so the odds of perfect emulation are better.
It'd be nice to see old atari 800 computer emulation, or even amiga, for that matter! (Both had some killer fun games, and both have been emulated well on the pc for a quite some time now.)