I use my PSP as an emulator device, since it has buttons... it has trouble with Star Fox 64, Perfect Dark, and Super Mario 64. I can't stand playing games that were meant to be played with a controller on a touchscreen, so I usually avoid mobile emulation. There are controllers out there built for mobile devices, though... and WiiMotes and Ps3 controllers can be bluetoothed in as well, so that's cool.
Perfect Dark is one of the best games on N64 indeed. Farsight XR-20 for life.