onepointone - 6:20 am on Nov 20, 2010 (gmt 0)
Twitter is no more "pure" than anything else. You can go to any freelancer site and buy tweets, facebook likes or endorsements, or whatever...not my cup of tea, but I've checked it out.
On the higher end you can buy tweets from celebrities.
There are even ad networks for them. Google: 'Celebs Paid to Tweet About Products'10K+ per tweet. (They are supposed to disclose their ad tweets.)