deadsea - 4:21 pm on Nov 14, 2011 (gmt 0) [edited by: deadsea at 4:35 pm (utc) on Nov 14, 2011]
If Google is trying to use this as a ranking signal, they will have to deal with some complications:
-- A lot of people will rapidly open a series of tabbed results by repeatedly jumping back to the SERPs page. They won't even look at any of the pages until they finish opening a series of tabs. This makes it appear that rapid bouncebacks are occuring when they aren't.
Google is clearly dealing with this. If I do a search, click on the result and then use the back button, I get a little notice in the SERPs to "block all <site> results". If I open many sites in tabs, I don't get this notice.
I believe that they have been using this data for years on a query by query basis: "Bounce back from your site for 'widgets' search is high, so you will lose rankings for 'widgets' in the SERPs".
I believe that Google started using this as site wide signal as a big part of panda: "Bounce back from so many search terms sent to your site is high, the site (or a section thereof) must not have high quality content at all."
-- For many sites a high percentage of the Long-tail traffic is mis-matched to the content of the landing page. The resulting quick bouncebacks are Google's fault rather than the website's fault.
That could be a problem. Google was directing users to the wrong page on my site a significant portion of the time a couple years ago. I actually started putting up big visible notices that said: "I see you searched for 'widgets', click here to go to the page that actually has widgets on it." Like netmeg, I am upset that Google is hiding referrer data from us. It keeps us from improving user experience for things like this.
[edited by: deadsea at 4:35 pm (utc) on Nov 14, 2011]