How to copy apps between 2 devices using the same Apple ID? Is there a way to copy an application from an iPod Touch gen.2 to an iPad 3G gen.1 while both devices are under the same Apple ID? The application is no longer present in the Apple Store.

Using iTunes is there a way to back up and restore individual applications?
When you connect the iPod Touch, doesn't iTunes offer to copy new purchases (i.e. the app that's important to you) to your Mac?

You can also try to copy the .ipa file straight off of the iPod Touch with iFunBox; http://i-funbox.com/ifunboxmac/