Here's my/our experience with Samsung and the RBE-- Had a 56" HLN model for a week or so before my wife decided it was too big. We both saw rainbows -- fairly prominent ones, but as described elsewhere many times, mostly in scenes where light and dark areas meet, and often in old B&W movies.
We then traded our 56" for a 50" HLP model which had just come out. I don't know if it was the size difference, the new chip difference, or the trained brain difference, but the rainbows were much fewer and far between. After a while, we didn't notice them at all. So I think there is definitely some eye-brain training that goes on subconsciously. We had that set for about 1 1/2 years, I think.
After moving recently, we've been watching a 19" LCD for several months, but just got an HL-S5688 two days ago. We definitely see rainbows, although they seem to be much smaller and more fleeting than when we first got our DLP several years ago. My guess is that the new color wheel and higher speed are the explanation. I'm also confident that after a few days, we won't see them any more.
If you absolutely want a no-RBE guarantee, get the LED-based model, or go with a different technology. I can tell you, though, that my wife is extremely sensitive in that area, to the point where she wasn't sure she could live with a Samsung DLP. But she now realizes that they DO go away (at least in OUR experience).