I see this as great news; my first reaction to hearing it was excitement. A lot of comments here are talking about the porn but outside of that, tumblr has a community with a uniquely sardonic sense of humor and is a platform for a host of independent artists and creators, and I would be incredibly sad to see it die. IMO Automattic will make for decent stewards of the platform (hell, anybody would be better than Verizon + Yahoo) and I have cautious optimism for tumblr's future.