MHes - 10:56 am on Apr 16, 2013 (gmt 0)
brokaddr - I think TheOptimizationIdiot is correct in a lot of what he says. I also suspect that Google just ignores spammy activities (e.g. keyword stuffing etc) and relies more on visitor behaviour.
Therefore, a site can have spammy stuff on the page but rank well because of good visitor behaviour. Perhaps the site you are looking at looks spammy, but it still provides the information required and your average surfer likes it. As someone who knows a lot about the subject of the website, you may think it is terrible, but many thousands of less informed people may accept it as good. Also, maybe there are a few very high quality back links which could make a big difference.
I think when you are looking at the possibility of Visitor Behaviour being a ranking factor, then I think it is only applied in relation to other sites in the specific serp. So, if Site A would normally rank just above Site B but the bounce rate is very high for site A then it will, in this specific keyword search, be demoted below site B.
Shocking Thought - If webmasters spend too much time clicking through and examining competitors sites, they just help that sites ranking!