What was the last life sign of Satoshi Nakamoto? I heard that the name may be a pseudonym and that very little is known about the initiator of bitcoin. Also it seems that he has stopped working on the main client. 

When was his last verifiable life sign? Did he ever mention or announce his retirement?
This was his last post on the Bitcoin Forums, December 12th, 2010. The day after he wrote this to the mailing list. As far as I know he did not (publicly) announce his retirement.