The hibernation and performance thread on Microsoft Answers which includes the answer above has more than 250 replies. The problem seems to be happening to a variety of models, running both i5 and i7 processors.
I asked Microsoft today for an update on what's happening. No word back so far.
Update: A Microsoft spokesperson said the company had nothing more to say beyond the statement from "BryanH" quoted above. The company also is not quantifying beyond "a small group" the number of people affected by this issue.