The upgrade process does backup the information and 3rd party appications on the phone. It does not take a backup of the OS itself. Not a big concern because you can download .114 from T-Mobile if you choose to downgrade.
Personal: T-Mobile USA Bold 9700 | 18.104.22.1683
Work: ATT Wireless Bold 9000 | 22.214.171.1244
Past: 8900, 8830, 8700c, 7100t, 7520, 7230, 7750, 6750