For example I don't know how it can handle the following (kinda conventional for a web app) situation: Multiple users, some are admins and some are regular users, with some shared "data" (like, an item for sale) between the two. Moderators can add/remove/edit items and edit/remove users, users can browse/buy items, etc. - I think if you're building an app like this, you really have to roll your own CRUDful server (with ruby or whatever)...
Oh, and BTW, RestKit[1] is probably much more mature and feature-rich than AFIncrementalStore.
[1]: http://restkit.org