I upgraded my iPhone to the 3G. The iphone had a few apps on it and when I sync my 3G after restoring the backup, none of my apps transferred over from my itunes. Even when I have downloaded apps straight from my 3G, when I tried to "transferred purchase" in itunes, it gave me this error pop up window:
Some of the applications in your iTunes library were not installed on the iPhone "My iPhone" because one or more errors occurred.