As far as the independence thing goes, based on what David said, Tumblr is going to keep on minding its own bussiness. I quote (again):
So what’s new? Simply, Tumblr gets better faster. The work ahead of us remains the same – and we still have a long way to go! – but with more resources to draw from.
According to him, Tumblr is just using Yahoo as an extra means of getting more money. Then again, I honestly hope that he stays true to his words and that Tumblr remains the way it is. Including freedom of blogging whatever the hell you want.