Ammon Johns at Cre8asiteforum posted an interesting topic named Google to target PR hoarders, where he discusses that Google might start looking to see if your not sharing your PR with other sites.
Most SEOs know that you can prevent PageRank from being passed to an other site by using a link that Google can not follow (JavaScript links). If Google can't follow the link then Google won't pass the PageRank, thus leaving more PageRank to be passed around to the pages you want.
Ammon quotes an old post by GoogleGuy at WebmasterWorld and then brings up current events that back this as a possibility for the future.
Check out the thread for more information.
