So I've just finished my first film edited in FCPX. A short horror, entitled "Mother Died".
We shot on Red Epic, I converted to 2k ProRes in Red Cine-X and then brought the files into FCPX to begin editing away at it. I have to say on the most part, it was a pleasure, up to and including the upload to YouTube without having to even leave the NLE. Seamless.
In answer to your question Scrubelicious, I edited on a current model iMac (i5) with 16GB RAM. FCPX performed wonderfully, from start to finish. I was incredibly impressed with it, considering it was the first time I'd used it.