We've been doing this for over a year. We're extremely familiar with all of the quirks of the process around push notifications and, during that time, have listened to what our customers are asking for. We've implemented most of these features and are in the process of implementing more. Using Urban Airship, you get things like autobadge (increment/decrement), quiet time (no alerts in the middle of the night for customers who don't want them), a super easy broadcast feature, arbitrary grouping by tags, scheduled notifications, the ability to hook up an RSS feed to automatically push notifications, and a web UI to send notifications... features like that, in addition to that, we have great support, so if something isn't work right you have a team you can go to get help.
A lot of our customers don't even have any server at all, they just use us.
On top of all that, we also have a great in-app purchase solution and rich messaging through AirMail.
It goes a lot beyond just a simple API to send push notifications. :)
