Whether the idea of push notification for the iPhone Facebook app makes you want to do a happy dance, or just run screaming for the delete button, according to a recently published note, you won't be getting it in the 98% completed Facebook 3.0 anyway:
Push Notifications, is in development but it won't make it into 3.0. You can expect it in a 3.1 update later this summer.
So what will Facebook 3.0 bring? The "new" news feed, ability to "like" status, events with rsvp, notes, pages, better photo management and browsing, a new home screen, fixed comment notifications, SMS and call from friends screen, and auto-save so incoming calls don't kill your unfinished messages.