I own a GP2X and I have tried this early Psx emulator. For an early release it is simply amasing. It can play Buster Brothers Collection at what seems like full speed with zero frame skip. Setting it to frame skip 3 makes it almost too fast or maybe im just not very good at this game. There has so far been Snes, C64 and Nes emulators (and others). A Snes emu that uses ASM core runs alot of games at either full speed or 90% but it currently has no sound. There have been Quake, Another World and Hexen Ports. I purchased this device because it is created for Homebrew, instead of blocking it like Sony they embrace it (more due to piracy).
I recommend the GP2X to anyone who is interested in Emulation, homebrew and ports. When the emulation on this portable matures I will no longer use my Psp for any of it. Almost forgot to mention the fact that nothing currently utilises the dual core so these emulators running at such good speeds are only using a single 200MHZ CPU so imagine what can be achieved by using both CPU's, not to mention the potential to clock each CPU to 266MHZ (so I hear).