just updated, but yeah, auto-dim (auto backlight) is defaulted to ON and is NOT on the option screen.
so far so good though, i followed the instructions to unlock the rest of the themes for the 8100
T-Zones work well enough and no need to reregister (on BIS, i have no BES)
no errors yet.
i'll answer any T-Mo upgrade related questions if need be.
edit: and oh yeah. your settings will be slightly modifed and you may have to reset some of them (such as wap.voice addition to apn, etc.)