It's possible, but the issue is that the sentiment is different for different sites. For example, if one of the sites I went to was a tumblr with smiling faces on it, and then I stopped going to that tumblr and I was less happy, the intermittent reinforcement wouldn't be the important mechanism. Some of the sites- like Facebook- were very much a "almost none of this is going to be interesting enough to devote time to, but at least it's novel" resource, and I don't miss them when I'm not going there. So the sites that I do miss must be giving me something, but it's not obvious yet what.