Flickr's a tough case. You make it Instagram or Facebook, even successfully, and it's not Flickr. I know I've personally bitched about Flickr stagnating but, when I think about it, I'm not sure how I really want it to change. It's a hosting--and, to some degree, sharing--site mostly for people who are relatively serious about photography. I can think of a few changes I'd like but I suspect that the original Flickr vision is fundamentally a niche market at this point.