If you just connect your iPhone to your iMac, then right-click it (in the left column) and choose to make a backup, it will create a backup of your iPhone as it is at that moment. So no need to transfer backups from one computer to another. I did this before syncing when I switched from iMac to MacBook and it works.How about this: can I transfer the iPhone's backup file from the MacBook to the iMac and then use the iMac to restore that backup to the iPhone?
It's kind of a hassle but I believe the original data has to be on both computers otherwise it won't let you sync all the same information as a security issue against piracy.
I threw caution to the wind, I guess -- and went ahead and synced. As long as the backup was on the Macbook, I figured I had nothing to lose. My big fear was NOT realized, so that's good (all the data in my apps were unaffected).
The only thing that was messed up was the folders on my iphone. Most of the apps were taken out of their folders, giving me about a dozen pages or more. There was still five or six folders -- each of them having, at the most, 2 apps. No big deal, it gave me a chance to a bit of re-organization.
All in all, it was a happy ending.