Google just issued a warning along with extensive “educational” information on the rights they reserve for sites selling links to increase Page Rank.
In taking their stance, they clearly state that they will uphold the quality guidelines set forth in their webmaster guidelines. Any site caught selling links to increase Page Rank will be dealt with accordingly. To quote Google they say “we reserve the right to protect the quality of our index.”
You can read more about this breaking story by going to their post titled
Information about buying and selling links that pass page rank