I'm a little late to the party on this one, but Marco Armet's inside look in to the acquisition of Tumblr by Yahoo is a great read:
Anyone who knows David can tell, very clearly, that he wrote every word of his announcement post. Not only did Yahoo let him end it like that, but the subhead on their official press release shows that Tumblr and Yahoo are seeing eye-to-eye on quite a lot already. In many ways, this feels more like a merger than an acquisition. This is clearly what David believes is best for his product. On such big decisions, he hasn’t been wrong yet. This time, though, I don’t have any doubts.
Marco was one of the driving forces behind the creation of Tumblr and his unique perspective on the company and it's founder is second to none.