I have been using RC2 fro a few days so far on an Intel i5 PC with win 7 64bit and 12 gb RAM.
So far I have nothing but positive reactions to what I am seeing, its as fast as (maybe faster than) RC1, the sliders are smooth and I am seeing near enough intstantaneous responses, adjustment brush and grad filter all respond well and the finsihed images apppear sharper (could well be imagination but thats what I am seeing, I seem to need to apply less sharpening to get the same finished image when I re-process some of my recent images.)
I'm liking the "Manual" adjustments in "Enable Profile Corrections" very much, a bit like having my own tilt & shift lens and find that with lenses such as my sigma 8-16 on kenko GGX 1.4XTC + 5Dmk2 it provides useful final adjustments
The only thing where I think it may be a tad slower is in rendering the image when switching from library module to develop module
So far, so very good
A little remark, perhaps somewhat pedantic
Actually, the manual horizontal/vertical transformations are equivalent to shifting the lens in combination with a varying camera angle (to neutralize perspective distortion). In contrast, tilting changes the plane of sharpness, which is not trivially doable in software.
P.S. Of course, LR cannot simulate shifting without varying camera angle (making visible what is outside the normal, centered image frame).