My Research - Push Notification in Mobile Ecosystem in 2011 - Gotchas - Part 9

Finally  the last final part telling about reliability of Push notifications.

Push Notification Gotchas

                        
 Push Notifications needs internet or Data connection!

Your recepients need to have data connection or internet on their phone to receive push notifications. You can not  identify the reason why your recepient didnt receive it.
 

Push Notifications Are Short!

You can only send limited data over push notifications. You need to have extra mechanism to pull more data from server.

Push Notifications Are Unreliable!

They are not reliable! There is no guarantee that push notifications will actually be delivered,

even if the APNS server accepted them.

They can be expensive!

Adding push functionality to your app is fairly easy and inexpensive if you own the data, but can be expensive if you have a lot of users or data you need to poll.