If you have a jailbroken phone, and use apps from Cydia, then you know how much of a pain it is to upgrade your firmware and redownload all your apps again. XBackup allows you to create a backup on your phone, and then sync that backup file to your computer via iTunes. When you are done upgrading and are jailbroken again, just go to the Cydia store, and download XBackup once again. Then in the app, run a restore, and your apps are back on your phone.
XBackup is available as a download from Cydia for $1.50 and is hosted in the Big Boss Repository. This may be worth it to you if you have a lot of jailbroken apps, and are tired of downloading them every time you restore or upgrade.