He's announcing that he's retiring. He had some health issues in 2006 so I really hope it's not related to that. Of course his consciousness will be uploaded to a positronic brain so he'll be around for a while yet.
If he was actually retiring, he's not the kind of guy to call that an "Earthshaking announcement."
Incidentally, I went to his last Stanford lecture, the lecture hall with maybe ~400 seats was totally full, and there were exactly 3 women in the audience.
