I did a full 2.3.15 SBF prior to installing the update via recovery and am glad I did, everything worked without a hitch, fully charged my extended battery and then used z4 to root my phone.
I have to say I am very pleased with the update so far, battery life seems to have improved a bit, no more battery manager force closes "yay!", the added quick search to the dialer is awesome and video speed seems to be smoother.
I've had all day to mess with the phone and had no restarts or real issues that I can think of, maybe I'm just lucky.