I have 4870x2 CF, and honestly, here's my opinion
1) It's fast
2) It's power hungry. Ridiculously so. I idle at >350W, full load>800W.
3) It's fast
4) It's hot. I don't need heating - I've got my computer.
5) It's fast
Oh, and did I mention it's fast?
That having been said, now that the 5870/5970 is out, I'd tend to lean away from recommending 4870x2 crossfire, even in the case that someone already has a 4870x2. The gains from the first one to the second one simply aren't huge (though they are noticeable), and you'll need a massively fast CPU to feed them properly. Microstutter isn't really a problem, but IMHO, wait a while and upgrade to a 5970 instead once the price drops a bit.