For Twitter to make the transition into a real business platform they will have to get serious about killing porn, spam, and scammers on Twitter.
Aside from being hard to find, your DM messages these days on Twitter are filled with four different kinds of spam and not much else. I rarely open the DM window, because if someone wants to say something real to me, they usually do it in public. They have the potential to score #klout that way. DM's should be reserved for direct communication between humans.
Dear Twitter: Publish the Limits. And arbitrarily enforced "variety of reasons" leads to more spammers not better Twitter citizens.