Andy Baio's been playing with Twitter's "promoted tweet" targeted ads, sending out tweets that are only seen by Twitter staff (hey, verify me already!), politicians (make better laws!), and, in one bizarre case, no one (a process Twitter calls "nullcasting").

http://feeds.boingboing.net/~r/boingboing/iBag/~3/qJWjrx7tbes/fun-with-promoted-tweets.html