This may have been mentioned elsewhere on the thread, but I'm wondering if the IM tour may have contributed to, or at least hastened, MP's departure. DT wasn't originally scheduled to tour much in 2010, but they had this opportunity that no rational band would pass up. However, MP wants a break from the band, and instead of a break, they get a summer of touring, and then they're in the studio in January.
Perhaps this might all be for the best. Assuming the replacement is as solid of a live player as MP, we might even see the return of the "Evening with" shows, which Portney himself stated he didn't like as much (on the Constant Motion DVD).