Tweetie sells for $3 without having to create and maintain any servers, and I imagine it sells pretty well. An updated Tweetie with your big honking refresh button and no push could probably still sell for $3.

With push, though, who bears that extra cost? Do the devs already have the excess capacity that the cost is trivial? Does Tweetie make enough money at $3 that the devs just eat it? Do they raise the price to cover server dev and maintenance? Release two versions, e.g. regular, and a “Pro” version with Push? Monthly subscriptions? A jailbroken version that pulls on a schedule in the background?

I am sure developers and customers will find the levels they are willing to pay, but it will be interesting when Push is released how this all will play out…