_Thumbs down on this. Facebook is not the new internet._
No, it isn't. However, if one's site is depends on social networking behaviors, like community-generated content, like this one is, it wouldn't hurt to use facebook's social graph to quickly generate content. Furthermore, as a suggestion, one could implement reddit and news.yc-style moderation on summaries, comments, and even authors to let the community decide quality books/reviews.
I actually differ pretty strongly on this point (and I plan on writing at length on it sometime). Just because Facebook's network stuff is relatively accessible does not make it the right choice for your site's social features. There are benefits to establishing the links that mean something to your website. I'm "friends" with a lot of people on Facebook, but I trust barely any of their book recommendations, just as one example.
The apps here (see below) don't look very businessy, and while the demographic I'm targeting isn't perhaps quite the same as existing summary sites, I don't think it overlaps a great deal with the lolcats type users, either. Are there "serious" facebook apps?
It isn't surprising that FB apps are not very serious, since FB is in its formative stages as a "real" website (one that is used for serious things, for arbitrary values of serious). I think that if facebook keeps growing like it is now, we will see the introduction of serious apps that in turn will attract more users, etc etc. Remember, 10 years ago no-one thought the internet will be used for serious things.
I won't knock FB for the advertising upside. But those 100k won't really be users of the service, which is what you really want for something so community-centric.
How many people signup for sites like these, and return rarely or never use any of the registration-enabled features? Are those "real" users as opposed to FacebookApp-enabled users?
I add an app in my Facebook. If it's popular enough, every few days I get a bump in my newsfeed from a friend who's actually using the app (albeit within FB). Splash some ads on the landing pages or figure out a freemium model, and all of a sudden it starts looking like a real business (embedded via iframe/fbml!).
