We do a lot of back end work for iPhone applications. When Apple started allowing push notifications we didn’t have a high demand for applications using this. However, in the last six months this is something nearly every application with a back end desires. We started using API on Rails. APN on Rails is a Ruby on Rails gem that allows you to easily add Apple Push Notification (iPhone) support to your Rails application. The hardest part is getting your Apple certifications sorted out.
We are in process of creating some patches to allow notifications to be sent using Redis instead of by rake task.