Flickr is a graveyard -- has been for some good time now.
That really isn't true you know. It achieves that balance between being centred on the photographs while retaining a very important social element better than any other site I know. There are other photo gallery sites, some of them visually very good, but socially they are pretty sterile. There are obviously sites which major on the social side but the photographs come a poor second.
I don't have any actual statistics, but anecdotally I'm seeing people who moved away from Flickr drifting back.
Yup, I'm one of them who drifted back. Tried 500px but decided Flickr was good enough for a place to store pics in decent quality incase someone wants to see my work. All I needed to do was clean it out a bit. The social aspect of it has been dead for a long time though, haven't noticed it getting any better.