Although I don't suffer from serious RSI, I've always favoured ergonomic keyboards because they offer an easy way to force myself to keep my hands in the correct posture to avoid wrist pain. The problem though, is that most ergo keyboards are chunkier and taller, which is bad for people who like laptop-like low profile keyboards. Microsoft's Comfort Curve 3000 is a meshing of the two ideas.
I've used it for about 2 weeks now, and find it quite pleasurable to type on. The feedback is similar to the Microsoft Arc I tried out last year, but a lot wider, because it's a full-sized system keyboard, and thus faster to type on.
There's enough feedback to make typing tactile enough, but not too much to make things super clacky. This, of course, is a subjective thing, so you'll want to try it out before you buy.
Adam Pash, who does have RSI, and also prefers low-profile keyboards, says this about his experience:
I used to have this bulky ergonomic keyboard but stopped using it, at least in part because it had the footprint of a boombox, and with the height of my desk, put my wrists at an uncomfortable angle. This keyboard's lower profile and small footprint has me giving ergonomic keyboards another shot.
One of the best (and most surprising) things is that it's only around $40. Microsoft has a cheaper keyboard - the Curve 2000 - but it doesn't seem as low-profile as this one. Note though, that it's wired USB, in case that makes a difference for you.
The largest complaint I have is that the arrow keys have no separation from the Right Ctrl and 0 key on the numpad, which means it's hard to move your hand over to the arrows by touch. You may get used to it eventually, but that takes a while.