What's up with all the Twitter spam?

From the moment Twitter made the public timeline searchable, the spam followers have been out in droves. If you mention a product name, that company begins following you. If you name a problem, someone claiming to have a solution begins following you. If you tweet about a job position, someone who’s unemployed starts following you. For the most part, this doesn’t really bother me that much. What does bother me, however, is the ever increasing number of MySpace-esque pornography spam followers I’ve been getting lately.