I am not an SEO genius like many people out there but I do know that I will only exchange links with Google PR that are equal or better than mine. Also one thing to be careful of guys especially when people are trying to sell you a link on one of their pages that has a ridiculously high Google PR is that there is a script/hack out there to artificially raise the Google PR bar at the top of your site.
I am always leary of people wanting to sell me a link. :shooter: