Twice now I have had other people's DMs appearing in my timeline. I have no idea who any of the other individuals are (they are not my alternate accounts or anyone I'm following). I can't imagine people will be too keen on Sobees when they find out that their DMs can be read by random people just trying to check their own DMs.

Screenshots:
http://twitpic.com/23tzpt
http://twitpic.com/233jn3
http://twitpic.com/233jeq