Designing for Push
When designing for push, keep scaling in mind. Normal computing doesn't need to scale. When coding is done, an app runs on a device using the local CPU. Should a developer deploy an extra 10,000 copies, there's no further investment involved other than increased technical support.
Push computing does scale. Whether you have 10,000 or 100,000 or 1,000,000 users matters. That's because developers must provide the service layer that handles the operations for every unit sold. The more users supported, the greater the costs will be. Consider that these services need to be completely reliable and that consumers will not be tolerant of extended downtimes.
Consider an application with just 10,000 users. It might service a million uses per day, assuming update checks every 15 minutes. More time-critical uses might demand checks every few minutes or even several times a minute. As the computational burden builds, so do the hosting costs. While cloud computing provides an excellent match to these kinds of needs, that kind of solution comes with a real price in development, maintenance, and day-to-day operations.
On top of reliability, add in security concerns. Many polled services require secure credentials. Those credentials must be uploaded to the service for remote use rather than being stored solely on the device. Even if the service in question does not use that kind of authentication, the device token that allows your service to contact a specific phone is sensitive in itself. Should that identifier be stolen, it could let spammers send unsolicited alerts. Any developer who enters this arena must take these possible threats seriously and provide highly secure solutions for storing and protecting information.
These concerns, when taken together, point to the fact that push notifications are serious business. Some small development houses may completely opt out of being push providers for apps that depend on new information notifications. Between infrastructure and security concerns, the work it will take to properly offer this kind of service may price itself out of reach for those developers. Third party providers like Key Lime Tie (keylimetie.com) and Urban Airship (urbanairship.com) offer ready-to-use Push infrastracture with affordable pricing plans. They handle the remote notification deployment for you.
On the other hand, many developers may employ push for occasional opt-in notifications, such as alerting users that upgrades are now available in the App Store or to send tips about using the product. How tolerant iPhone users will be of this kind of use remains to be seen.