Apple has just seeded iPhone 2.1 beta 4 to developers-uninteresting, really, except for the fact that the push notification service has been pulled from the release "for further development." Targeted to hit your iPhone in September, the push service allows apps to receive notifications in the background while they're not running, a godsend for AIM and other messaging apps. Hopefully this doesn't mean it'll be delayed, but we've all learned what happens when iPhone software rolls out before it's finished baking, so I'd rather wait. [Mac Rumors]
Not to be annoying or what not, but it should be pointed out this has nothing to do with Push via Exchange or MobileMe (IE, contacts, calendar, email) - but rather Push for notifications for AIM and other applications. Something that will become -very- useful. And like others have said, not point in having the code in if it can't connect to a server.
That being said, I will be sorely annoyed (which doesn't amount to much I suppose) if it isn't in the september release.