Facebook CTO Bret Taylor, who once described himself as being in “violent agreement” with Mark Zuckerberg, is reportedly stepping down later this summer to work for an unnamed startup. Taylor has been a leading figure behind some of the most familiar innovations in the last decade – Google Maps, Facebook’s social plugins and Open Graph. His decision to abandon Facebook for a startup is an ominous sign for a company that, until its disappointing IPO, was considered an unstoppable juggernaut.