But with tabbed browsers and no access to site stats (unless the site in question is running GoAn, maybe), they can't even measure time on site accurately. Not that
anybody can, really, but you're in a better position to at least give it a shot if you have access to the site logs or other analytics, which Google does not for a whole bunch of sites out there.
The popularity of GoAn notwithstanding, they haven't achieved 100% coverage... yet.

I use FF and IE7, both of which offer tabs. When I'm searching for something (not for a specific site, but information or a product that might be found at multiple places), I tend to click on however many results from the first, maybe even the second or third, page(s) that look "promising," opening each in a new tab. One right after the other, just working my way down the SERPs until I see the quality of the results obviously drops off or I judge I've got enough samples that it's likely one will fill the bill.
If I find what I want when I go back and review the tab contents, great. If not, I have a "multi-search" toolbar in FF, and I'll more than likely go there and start a whole new search rather than open up that original Google SERP page and refine the results from there. In fact, I may have already closed the tab that contained the original SERP by then.
So, depending on how you look at it, I
always "click right back" to the original SERPs no matter how relevant and useful the pages I've selected might be (if you decide each consecutive click means I've visited that page and am now immediately coming back to look for another because the first page was crap -- an incorrect assumption, of course, but one which might appear reasonable considering the click behavior viewed in a vacuum) -- OR -- I
never click back to the original SERPs no matter how irrelevant and useless the pages I encounter turn out to be (if you correctly deduce what I'm doing with the initial clicking behavior, and you're sitting there waiting for me to come back and refine my search criteria on that same SERP, which I almost never do).
I think the folks at Google are smart enough to figure out the inherent issues with using those measurements in any significant way to actually influence rankings. I'm guessing at least a few Googlers use FF for browsing, themselves, and I can't imagine I'm the only person in the world who's discovered this handy little multi-tab search method.
Not to mention how simple it would be for somebody to boost their pages' ranking simply by hiring people to click on those pages in the SERPs for desirable key phrases, never returning to the original SERP (therefore leaving Google to think -- should they be measuring something like this -- that the page in question was completely relevant to that searcher's query such that no further searching was necessary).
If it's a GoAn site, you then close the loop by having these paid shills click through to an internal page or two, so Google (if they're looking) can see these "searchers" further exploring a -- presumably relevant and useful -- site which they reached from this -- presumably relevant and useful -- entry page. Lather, rinse, repeat for a few hours each day, using various proxies and ISP accounts to conceal who you are.
Voilá. Instant "relevance."
The folks at Google are so concerned with their results being artificially manipulated, I find it difficult to believe they'd leave such a honkin' big -- and OBVIOUS -- loophole wide open and inviting abuse. I mean, if a humble webmaster like me could come up with this plan in a matter of minutes, just think what some experienced blackhat with some mad programming skilz and a bit of time on his/her hands could devise.
Of course, I could be wrong. Google has done dumb things before, and I'm sure they'll do dumb things again in the future (as will we all, come to that). But somehow I doubt if they've been quite
that dumb in this instance.
My

--Torka