This from the AP:
Don Mattingly stepped aside as the Dodgers' hitting coach on Tuesday and was replaced by Mike Easler. Mattingly followed Joe Torre from New York to Los Angeles and was supposed to eventually replace Torre as the Dodgers' manager. However, he said he needed to go home for family reasons. He will remain in the organization as a special advisor and coach. "I'm very grateful that the Dodgers have allowed me to take care of these family matters and I hope that everyone can respect our privacy during this time," Mattingly said in press release. "I truly appreciate the support of all Dodger fans since joining the organization and I look forward to helping the team win in 2008 and beyond."
I assume he left to mourn the death of Heath Ledger...but that's just speculation.