I have owned a GP32 for about 4 weeks now and is easily one of the best purchases i have ever made. The PC Engine emulator alone is well worth checking out. I have got on my GP32 (128mb SMC):
PC Engine emulator + around 30 games. (full speed and sound)
SNES emulator + 3 games (75% speed no sound)
GB GBC emulator + around 70 games (full speed and sound)
Atari ST emulator + 2 games (full speed and sound)
*Doom - Ultimate Doom and Doom 2 (full speed and sound)
Mya Mya Rocket (good game, Chu Chu Rocket clone)
C64 Emulator + around 20 games (full speed and sound)
King Of Fighters '91 - Excellent Beat 'em up
CBM Plus/4 emulalor + around 20 games (full speed and sound)
*MSX emulator + around 50 games (full speed and sound)
Sega Mega Drive emulalor + 7 games (75% speed no sound)
NES emulator + around 20 games (full speed and sound)
2 Spectrum emulators + around 30 games (full 48k emulation at full speed and sound, partail 128k emulation)
GPPang - Excellent Pang clone
GPasteroids - Excellent Asteroids clone.
Early Arcade emulator (8080) + 7 games (full speed and partial sound)
*Colecovision emulator + around 10 games (full speed and sound)
*Sega Master System and Game Gear + around 80 games (full speed and sound)
A couple of MP3s
*Can suffer from split screen bug but easily dealt with on menu (select no double buffering on video options).
Also a Metal Slug demo has just been released, and also a GBA emu is on the cards and is reckoned to be very excellent (maybe full speed and sound) because both system share same CPU, but GP32 is clocked WAY higher! Make no mistake, a GP32 is definately a machine to be reckoned with!