There a couple Urban Airship cofounders that read HN, myself included - please don't hesitate to ask us any questions. This has been a really, really fun project with some very interesting technology coming out of it.
Urban Airship is a great product, we use it and it really reduces a lot of headaches. There's really no reason to try and lay all the pipe yourself, particularly if you're just getting started. And furthermore, Urban Airship picks up where Apple leaves off with a lot of nice features you'll find you need later.<p>Their team is also super friendly and responsive. We've sent multiple support emails with answers coming within hours.
The TC article doesn't mention the In-App Purchase features you offer. It sounds like you offer free-for-the-user updates to applications as well as providing infrastructure for traditional in-app purchases managed through Apple's billing. I'm curious about how you bill for these features if you don't mind taking a moment to explain.