As mentioned on Sara Goleman's blog today:

Incontestably the driving force behind PHP6 [...] Andrei Zmievski will be taking off for San Francisco to join a fresh young startup. Andrei's been a pivotal member of the PHP community for the majority of it's life.

As far as she knows, though, he's not moving away from working so heavily with PHP and the development group, but his employment move and setup time at the new company could cause a bit of downtime.