I've got one on my 9800Pro. It works fine, my card o/cs to 425/365 stable. Runs most things fine at about 475/365, but it'll artifact in really heavy-duty 3D.
It gets *really* hot while it's running under load, though, and the heatpipe doesn't cool the memory. I just ordered the fan to go with it (the OM-12 or whatever), so we'll see if that helps.