Q: I own a second-generation iPod touch and I’m thinking about upgrading to a third-generation model. Will I be able to use all the apps I’ve purchased for the 2G touch with the 3G touch without paying for them again? In order to do so, would I first have to delete them from my 2G touch?
A: You can use your purchased apps on any number of iPhone or iPod touch devices that are synchronized to one of your authorized computers. When upgrading to a new iPod touch or iPhone, you simply need to connect the new device to your iTunes library and set it up as you normally would. Any applications that you have in your iTunes library can be automatically synced to the new device.
Note that by default, this only includes the applications themselves and not your actual application data. However, if you’re replacing your old iPod touch with the new one, you can simply restore the backup from your old iPod touch via iTunes, and in fact iTunes will prompt you to do this when you first connect the new iPod touch:
Restoring the backup from your existing iPod touch will also restore all of your sync settings in iTunes, so this should set up your new 3G iPod touch to behave identically to the way your old iPod touch was configured.
Note that you do not need to remove the applications from your existing iPod touch before syncing them to the new device. There is no limit on the number of iPod or iPhone devices that can be authorized for a given iTunes Store account and the iTunes Store does not actually keep track of which devices you have your apps installed on. Note that you can only have content and apps from up to five different iTunes Store accounts stored on a given device, however.