Ohm. Well thanks. Flickr isn't bad, but DA is way more social I find. MP is ridiculous, and Facebook just doesn't lend itself well to MOC groups. Not to mention some other issues I won't get into out of respect.
I've never used brickshelf, so I wouldn't know. Can people even leave comments or feedback on brickshelf? THe only thing it's got going for itself is the multiple photos thing, and both flickr and MP have that. DA is working on something like that though. I suggested it in one of the site update things and one of the people who work for DA got back to me and said they're aware the feature is needed, but that they're working out the technical shit.