I got a link on www.boingboing.net this week, which if you haven't heard of, is one of the most popular blogs on the Net with a PR9 homepage. The link I got was a thank you for suggesting a story and not very prominent (my name is too short) but hey it was on a PR9 page for a bit. That link sent me a total of 18 visitors. In the long run it may do me a bit more good but from a traffic point of view not so good. So lessons learned for me, help other sites by suggesting good relevent stories and they'll often thank you with a link. Don't expect a lot of traffic just because the page has a high PR which I kind of already knew and must admit I don't really care about PR but still get excited when it updates .
Link exchanges almost never give you traffic up front...but your search engine rankings will be great over the long run
permanent links get you more visitors over time. Had the link stayed there, you might have had 20 or so users visiting your site everyday. But the link from their site will help increase your PR in the long run.
One thing I have noticed in recent times that high PR site can give you as a good backlink but it doesn't mean that it will give you good referral visitors as well.