DeJean seems like a decent pickup. They were getting rid of Karim anyway, and they can use all the help they can get in the 'pen. Since leaving Colorado, DeJean has had ERAs of 2.78, 3.12, and 4.68. His K/9IP rate has been in the 7-8 range, and is over 8 this year. He's always walked too many people, but it's not ridiculously out of control. I think he's just had a little bad luck this year, and should bounce back to be servicable down the stretch.
 
All that said, he's ranked as the second worst reliever in baseball this year by Prospectus' Adjusted Runs Prevented.