I get that it's a "passport to a social network of great applications". But, as far as I can tell, that social network is still centralized, no? Am I missing something?
Yeah, it's centralized. It's a storage space with a nice API for putting contacts, conversations, photos, etc. Edit: it also has a nice big "export data" button that will dump all of your data from all app.net applications you use.
If I'm motivated to move away from existing social networks for any reason, it's because they are centralized...
The fact that app.net is/was pay-to-play doesn't eliminate the issues of free-to-play at all: it still has the same issues (and moreover: less virality) but now I'm paying for them.