David, I would agree. LR 3.5 has settled down very nicely on my Win 7 64-bit machine, and at last it seems stable and quick. So I, for one, am certainly in no hurry to upgrade to anything.
However, we can deal with all of this on a no-risk basis (at least initially). When LR 4.0 final comes out, there will be a thirty-day trial. So we can see how the thing beds down before we lay out any cash. I wish I had done that with 3.0.