actually this is a question I've recently come up with. Does linking "to" a PR7 or higher site (if it's related to your site and userful to your users) have any value? I mean I'm going to put it there anyway because it's useful to the users but I'm just wondering if linking (non-reciprocal link) to a highly ranked site is useful (in my case linking to the state departments travel page which has a PR8).
I guess it should help (pure guess) my logic is that you are giving a link out to your highly ranked competitor in order to serve the internet user and that is want google wants (user centric quality links). Please correct me if my guess is wrong and misleading.