Apple made a big deal about allowing in-app transactions with the new iPhone 3.0 API. It's great news if you're a developer looking to make more scratch, but it's potentially terrible news for users.
Basically, this is opening the flood gates for nickel-and-diming microtransactions from the App Store. Before, when you spent $5 on a game, you knew you were getting the whole game-with free upgrades. Now, you'll spend $5 on a game and you'll need to spend another $5 to unlock all the levels and weapons. And that's on legit apps. Just wait for the novelty fart apps with one fart sound that want you to pay for extras, or a flashlight app that wants you to pay for different colors.