The DS is too slow to run UAE comfortably. It would not be a very satisfactory experience. If you want a DS and want to run homebrew, I recommend buying the M3 Simply, which lets you run homebrew software from a micro SD card. The DS is a lot of fun. I love mine.
If you are after a portable Amiga experience look in to the GP2X.
Here is a Quicktime video of Nebulus running under UAE4ALL on my GP2X. As you can see it runs *very* well.
--
moto
