"There are purchased items that have not been transferred..."

Several of us have complained in another thread ("How to Update") about getting a message that says, "There are purchased items that have not been transferred to the iTunes library" when we try to update to the new iPhone software. I have a 3G and a MacBook Pro running Snow Leopard. The problem is that no matter what we try to do, our phones don't seem to "clear the warning," suggesting that something is still on the phone (a purchased item to boot) that hasn't made it to the iTunes library.

Does anyone have the solution to this problem, or a workaround? I apologize if this has been effectively addressed elsewhere, but I can't find it, and apparently I'm not the only one.