Google would want to use information that would be relatively uniform over its entire index. Clearly, not everyone has Google Analytics installed, nor are the installations uniform, so that in itself would make it a bad choice to use.
I doubt that they use it even for manual audits, but I'm sure they're in some way looking for big data correlations on the installed base that might help them confirm patterns they're seeing in other ways.
Perhaps they check aggregate correlations on types of sites to suggest ways of improving both Analytics and the algo. Too "noisy", though, and too invasive, as a ranking metric.
Well as a bonus using GA I was able to see traffic drops in our site, but using it we opened our sites wealth of information to G and that combined with other metrics pagespeed, over time, (G wants a fast web) they could determine what is the proper bounce for that search term. And delivery results based on the bounce metric alone.
What made me bring up this question is I have noticed very funny issues with the back button going to some sites via G being disabled and having to hit it multiple times to go back, little things like this could easily lower bounce rates, by having people kill the window, rather then bouncing away. Or leaving that window open for an extended period and opening a new window.
@Pjman so one bad site still sinking, 2 with good are rising.
If you have a network of affiliate sites that are yours, it's a kiss of death. Other's will disagree however I have proven it for myself.
mrguy - Are you talking about the shared account, or are you talking about information Google is extracting about your site performance? I'm guessing it's the network aspect. Did the sites share hosting?
That first part, UA-1234567, if you keep all your sites in the same analytics account, is the same. And, it's in their cache, so Google doesn't have to do anything special to identify a shared network of sites.
The easy way 'round with analytics is just to create different user ids for each site you put into Analytics, then grant them all access to a single account. That's safe enough, unless you think the they are pulling account data for SERP ranking purposes.
The similar issue with adsense publisher ids is a little harder to work around, but there's a couple of strategies that work.