Photographers and enthusiasts have been drifting away from Flickr for ages, but up until now there's been no offering that's really a suitable full replacement.
On the one side you have sites like SmugMug, which has an awesome API, detailed controls over your images... but is devoid of any of the social features Flickr users have grown to love (and loathe sometimes - YOUR PHOTO HAS BEEN INVITED TO [INANE GROUP HERE!]).
Or you have beautifully designed sites like 500px... which also has no API and forces its users to operate the whole thing painfully in manual. But it does have really good discoverability features, maybe better than Flickr.
I'm not confident that Facebook and Google+ will take over the photography enthusiasts' world. I believe that most regular people will share their pictures there (and they already do, on Facebook), but the photography community won't jump on board until there are some very significant leaps (solid API, discoverability features, more niche-specific social features).
But in any case, Flickr is feeling old and creaky, we're all just waiting for something better to come along. Honestly, I'm surprised it's taken this long.