Supposedly there is a new Flickr being shown off tomorrow and hopefully Yahoo rebuilt the site from the ground up.
In a lot of ways most people are looking for what Flickr offers but refuse to use it. They want privacy, a place to back up their full-resolution smartphone photos and for a very cheap price.
Yahoo may be better maintainers than innovators, but I'd rather have seen posterous acquired by Yahoo and maintained than acquired by Twitter and killed.
For the existing team at tumblr (say anyone who has stock that is) things like this end up being a buzz kill after it settles in. Working towards something is fun and motivating. Once you get it things simply change (speaking from personal experience and observation here (also as you are pointing out).
For example, would you like to get paid now for all the work you are going to do for the next 10 years in advance and still find it as fun and challenging? If you were an athlete would you want to know in advance that you were going to win 2 medals in each of the next olympics? To me that takes the fun out of things. I think it's obvious why things are different after money changes hands.
In this situation how do you show up for work at twitter and still be creative after essentially the "game", if you want to call it that, is won? You will probably itch to get over to a new challenge. Not to be cliche but the journey is a big part of the picture.
Its obviously very hard thing to do, but I am (probably the only one in HN) rooting for Yahoo. Tired of 2-3 companies dominating the tech world. I am rooting for Marissa Mayer to succeed and give others a run for their money by doing an epic u-turn with yahoo and changing everyone's perception of what yahoo is usually associated with.