To be honest, UAE on the gp2x is not perfect at the moment, although it's getting better. Speedball 2 requires the sound to be turned off otherwise it has random freezes (unsure if this is a problem on Windows?).
Overall though the system is super cool, not to mention the guys on the GP2X forum are friendly and theres a good fun atmosphere. No one seems to regret their purchase. In addition to Amiga, you can emulate Atari (2600, 7800, Atari St), Vic 20, Commodore 64, Megadrive, MAME, and many others. It's like the ultimate retro gaming device in your hands.
Note: The GP32 is the old system, the GP2X is the new (go figure!). See:
www.gp2x.com