I don’t have much to add to this at the moment, although given my current involvement with the real-time web obviously I have some thoughts on the matter, but I found this analysis of how social applications are built in contrast to how action-oriented Google applications are built to be rather interesting, particularly this part as it relates to real-time features:
Quora is a dozen people running dozens of experiments in how to optimally use bacn to get people to return to Quora, and how to use toast to keep them there. Bacn is email you want but not right now, and Quora has 40 flavors of it that you can order. Quora’s main use of Bacn is to sizzle with something delicious (a new answer to a question you follow, a new Facebook friend has been caught in the Quora lobster trap, etc.) to entice you to come back to Quora. Then, once you’re there, the toast starts popping. Quora shifts the content to things you care about and hides things you don’t care about in real-time, and subtly pops up notifications while you’re playing, to entice you to keep sticking around and clicking around. Some toast is so subtle it doesn’t even look like a pop-up notification—it just looks like a link embedded in the page with some breadcrumbs that appear in real-time to take you to some place on Quora it knows you’ll find irresistible. For every user’s action, bacn’s and toast’s fly out to others in search of reactions. (Aside: if I were Twitter, I would be worried. Real-time user interfaces are more addictive than pseudo-real-time interfaces; what if Quora took all of its technology and decided to use it to build a better Twitter?) Social apps are action-reaction interaction loops; Google apps are designed just for action.