What are the main differences of showcase websites like the ones mentioned on the title of this question?
I've never used any of them, and I'm not really sure what are the main differences between all of them, being them technical (what you can and can't do with them), by intended usage or by the what their users made them (social networking websites tend to acquire their shape and differentiate from each other even by the habits of their users).
By browsing them and reading the descriptions on Wikipedia, I can't really tell what these differences in the intended usage are; I can only guess that DeviantArt seems more oriented toward amateur artists while the other two seem to be geared more toward a professional audience.
If there is somebody here that has more experience about them, I'd like to have a brief comparison of these sites (and even other similar ones, if they exist, I've only mentioned the ones that I know of).