And despite the fact that Forstall stressed that today's iPhone push notifications are brought to us by the word "scalable," there remains the question of just how much Apple's system can handle. Could millions of Twitter updates--say, at an Apple event--bring the entire service to its knees? If there were , how does that bode for the notification system?

The amount of time Apple spent at last year's WWDC and on Tuesday's event explaining why push notifications are superior to background processes suggests to me that the latter is in fact what Apple would prefer to be doing, but the hardware just isn't there yet. The push notification system is a stopgap solution, just like Steve Jobs's claim that web applications were "a pretty sweet solution" for third-party developers who wanted to write software for the iPhone. Over 800 million App Store downloads later, we all know how well that turned out.

The real question is: are push notifications good enough to keep iPhone users happy until a more capable solution is possible? We'll have to wait until this summer to find out--well, assuming it actually ships this time.