A fantastic emulator, I must say. Games that ran horribly before on gpSP run nice and smooth on ReGBA. I have, however, noticed some issues with several games. The most recent issue being from Dragonball Z: Buu's Fury.
Using the stock GBA BIOS (to test with gpSP, since Normmatt's seems to not work with gpSP), BF runs fine, albeit a little choppy and requiring the use of frameskip. With ReGBA, it runs nice and smooth, but will crash from time to time, seemingly randomly. I've seen it crash while transitioning from menus and dialog boxes.
With Normmatt's BIOS, it's stable, but the graphics will get completely garbled and render the game unplayable. As mentioned before, gpSP boots to a white screen when using Normmatt's BIOS.
I mentioned this on the IRC as well a little earlier, but I figured I'd mention it here too. Other than a few complaints with a few games, I love ReGBA and vastly prefer it over gpSP for most games. Great work so far!