While most Mac users are well aware of the uses and benefits of a marvelous little program called Growl (In case you already did not , it is a notification software that very easily attaches itself to almost all the common Mac softwares), the good news is that the makers of Growl have extended the usability of their useful App to the iPhone as well. Now you can get your tweets while you are listening to that favorite song of yours.
Prowl is a Growl client for the iPhone. Notifications from your Mac can be sent to your iPhone over push, with a full range of customization and grace you expect.
Push notifications As soon as a Growl notification pops up on your Mac, Prowl will forward it to your iPhone or iPod Touch over the push notification service found in iPhone OS 3.0. Which notifications are pushed is configurable, allowing only the important messages to be delivered.
While the list of features is really not over the limit but frankly it is enough for everyday use.
Prowl also features a small but excellent selection of sounds which can be played when your push notifications arrive.
Yes it really is just that simple!
The possibilities really are endless: You can be pinged with a push notification when a torrent finishes downloading, you get a new IM or email, you’re mentioned on Twitter, or anything else Growl can notify you about.
The cost for all this $3 only. Yes that is a lot less for an App

Its really nice that we have Growl notifications on the iPhone too! But it would be much better if the app were free of cost, like Growl.
I think it is more to do with Server costs to push the notifications!