As of now there is two kinds of apps in the app store. iPhone apps that can be used on an iphone or iPad and iPad apps that can only be used on an iPad. The iPhone 4 is going to ship with a built-in three-axis gyroscope. I have a feeling that developers are going to heavily utilize this function in games. This means that there is going to be a bunch of apps that can only fully work on the iPhone 4, almost a third category. Kind of odd that Apple did not introduce this with the iPad. There will be a bunch of apps in the coming months that will have features the iPad cannot take advantage of. I love my iPad so far but will be getting an iPhone 4 when it's released in Canada. If developers start utilizing the gyro in games I can't see myself getting the iPad version without this function.