There's been a lot of talk over the years (especially post Panda update) about whether or not Google uses bounce rate as a ranking signal. In fact, even this morning at SMX Advanced in the SEO Periodic Table session, the topic came up. Here are a couple of tweets from an attendee of that session:
Apparently, Google's Matt Cutts said flat out (via second-hand news) that Google does not use Bounce Rate. Danny Sullivan just tweeted:
Common thinking seems to have been that bounce rate is not a ranking signal, but this could help put a stop (or at least add a major point of argument) to the debate.