Hi Aaron, I’ve been wondering that as well. I also have watched as colleagues/friends that would normally post their content on Flickr with a CC-license are now opting to post their art/photos on their site and leave a CC license. A good example of this is the work by the great Bryan Mathers (http://bryanmmathers.com/).
I think there is a challenge because some might only discover/use your work by searching in Flickr. I also think there is better ownership of your work and control of it online.
I think with the Instagram question I would recommend sharing your work in a couple of places. I’m thinking about starting a Known feed that archives all of the screencaptures, screencasts, and photos I share and use. I would also share this out on Instagram and Flickr as well. The spot on my website would be to archive and keep a trail of all of this. The Flickr and elsewhere would be to connect with others.
My concern is that at any point these other services could disappear. I don’t want my work to disappear as well.
Hope that helps.