IMO google puts alot of emphasis on the anchor text of links pointing to your site. So having 500 sites linking to you with “online casino” is better than having 1000 linking to you with things like “this site” or “my friends casino site”.
BUT in the above example the site with 1000 links will have a higher PR (theoretically) but the page with 500 links will rank higher for the term “online casino”.
What i’m trying to say is that the number in your PR means absolutly nothing, but if you’ve got a high PR and every site that contributes to your PR links to you with the same anchor text, then guaranteed you will rank higher than any other site with a lower PR. Guaranteed.
This is why it’s better to have a few good links, than heaps of crappy ones.