Hi. I just wanted to make a few comments on the idea of using the Google tool bar to track how long people stay at websites. I think it would be a great idea, and would be a great indicator of site quality, until SEO people found a way too cheat with it.
Now imagine a website where a person could go to download this JS program, or toolbar, and get paid x amount per each site this program (or tool bar) navigates to (and stays at just long enough to trick the Google tool bar into thinking a visitor came to this site and stayed for a while). Thousands of people would get this program and let it run all night, if it made them a few bucks.
Finally, imagine an ad that was titled, "1000 unique page visits, each 1 to 2 minutes in length, only $20! Great for Google site popularity!" Companies everywhere would be offering this service to SEO people, and SEO people everywhere would be using this service, because it would boost their SE rankings.
BTW, "site popularity" would be quite similar to the already existing "link popularity" or "page ranking". It would be another factor in the algorithm used to determine SE results ranking.
You see where I'm going with this? It would be way easier to cheat with "site popularity" (as determined by the average amount of time a visitor stays at the site) then it even would with link popularity.
I'm going to say it again. The answer to making SE results truly relevant lies in making SE robots more intelligent--in the way they analyze individual pages. I think the recent occurences at Google is evidence that SE companies feel the same way. Google realizes that when a person makes a query and visits a page the query turns up, they don't care about keyword density--they're not counting keywords. And they don't care about how many sites link to this page, either. All they care about is whether they find the information they were looking for, and equally as important, whether or not that information is displayed in ready to use, human form--and not SEO form.
Of course keyword density and link popularity are important, but I think they will become less important as SE robots become more intelligent. And they will become more intelligent.
Just my opinion
P.S. I know that SEO and site usability go hand-in-hand, or at least they should (in a perfect world).
So no lectures about that, please.