Tapulous has issued an update to their Tap Tap Revenge rhythm game which includes working push notifications, despite the fact that iPhone OS 3.0 isn't officially available for two more days.
It certainly isn't the most creative use of background notifications—the messages only pop up when you're challenged by another player—and I'm already wondering how, when all kinds of apps have this capability, the iPhone's exceedingly simple notification system will scale.
OS 3.0 users can give the free app a try now, but keep in mind that we'll probably see more than a few push-equipped apps rolling out in the next few days, as I'd imagine Apple will want to have a few high-profile 3.0-capable downloads available at launch. Alternatively, if downloading the app, getting a friend to download the app, and having him challenge you to a Lady GaGa tap-off is a little too embarrassing for you, just watch the video below. —Thanks, Tim G! [Video from 9to5Mac]