Got my GP2X this morning and one of the first things I did was set up UAE4All. I'm seriously impressed with the performance.
Here is a Quicktime movie of me playing one of my favourite Amiga games Nebulus on the GP2X. As you can see it runs just as smoothly as on a real Amiga :-D
Note - the file is about 40MB so it would be best to download it before playing.
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moto