Well, considering it's an activity that Google frown upon and are quite aware of, I'd actually recommend against buying links.
Even guest blogging has been denounced as a waste of time by Google's head of webspam, Matt Cutts, with the reason being that so many spammers have taken up "guest blogging" that Google has stopped giving those kind of links any importance.
The same goes for link directories and all the other black hat seo tricks from 2005.
If you want to trick Google, at least think of something more innovative and current than buying links!
