* It's becoming clear that Facebook will remain aggressive in protecting its turf through new products and big acquisitions. Facebook's Instagram purchase didn't turn out to cost quite the $1 billion it seemed at first, but it's still a huge bet on a service that for all the world looks to be on the growth trajectory Facebook was several years ago--and a signal that Zuckerberg will buy crucial new services that his engineers couldn't build. And with the release, albeit somewhat controversial, of a new feature called Poke, a mobile messaging service apparently intended to blunt the popularity of Snapchat, Facebook is sending a message that it will let no upstart steal a march without a fight.