http://uk.tv.ign.com/articles/114/1140763p1.html

Here's a story with a strong sense of déjà vu. It was just a year ago (and one day!) that news broke that Dexter's longtime showunner/executive producer Clyde Phillips was leaving the series, on the heels of Season 4 ending. Now, the week Season 5 has concluded, Phillip's successor, Chip Johannessen, has made a quick exit from the series after a single season.

Deadline broke the news, revealing that Scott Buck has been named the new showrunner going into Season 6. Buck taking over is a different approach than when Phillips departed. In that case, Johannessen was completely new to Dexter, moving over to the series from 24.

Buck on the other hand is being promoted from within, having been with Dexter as a writer since Season 2. In those years, he's moved from co-executive producer to executive producer and Deadline says he has "great rapport with the show's writers," noting that he had served as number 2 to both Phillips and Johannessen - and that while Johannessen is well regarded, Buck "was ready to take the reins of the series."