the site relies on pretty much everyone being part of the site for it to be effective and checking it 24/7 to see if someone noticed them. Which is just never going to happen.

Yes, it's going to be a pageview generator, since you'll have people early on checking 100x a day to see if someone mentioned them, but give it a little time, and that'll stop since chances are noone will notice the post.

And this is why they mention the 20 million page views number instead of their uniques number.

That's true but they are only 6 weeks in. If they can do this, they can probably add new interesting features which get them loyal users over time. I like to be hopeful rather than cynical by default.

Edit: I just realised you still didn't answer my question. I ask it sincerely: What dynamics do you think it needs to have staying power?