I think I'll be giving RA a try... for several systems, anyway. I watched a few videos, and it doesn't seem too terribly complex. As for the UI, it's not great, but not garbage either. However, while I won't say the PS3 UI is "bad" (lordmonkus), it's far from my favorite, and does sometimes border on irritating to me. But it's not like I should be spending too much time in it, right?
As to your warnings, snarfo67, points taken, thanks, but they don't really apply to me, especially the controller stuff. I'm just setting up an arcade cabinet with a tankstick, and the only console games I'll have on it will be appropriate to those controls, or easily adaptable. If I want to play something odd, I'll just go pop a cartridge or disc into the actual console.
Now I suppose i need to decide which systems to use RA for. I think Atari 2600, NES, SNES, N64, SMS, Genesis, Saturn, and PSX. Then use MAME, Daphne, and NullDC or Demul, Does RA have a good Atari 400/800 core?