[sokoloff]

They are indirectly penalized for it. Bounce rate is a factor in google's organic search algorithm. If a lot of users click-through a given search result, find a bad experience, google has incentive (and makes an effort) to penalize those results.

[ForHackernews]

Wait, how can google measure that? Do they have a tracker that sees when I leave a site?

[sokoloff]

They get direct data on click-back. (Search, click, come back to google after a very short time, is a fair signal, in aggregate, that the users don't like that site's search results or other experience factor.)

I don't believe they directly have bounce data, but they infer it from click-back. They have publicly stated that they do NOT use google analytics data to inform organic search rankings.