Just did the update. Downloaded quickly over WiFi and took about 2min to install.
I was: Rooted (Universal Androot) and with Rom Manager, Koush Bootstrap, but otherwise 2.3.15.
[Results]
All looks good! Except I lost root. (no surprise).
Universal Androot (1.6.1) does NOT work.
Z4 Rooted just fine
Clockwork Recovery still installed and working (!?)
Boots 4 seconds faster.
Seems to take longer to load widgets (never timed my time-to-fully-booted)
[Versions]
System: 2.3.340.MB810.Verizon.en.US
Android: 2.2.1
Baseband: BP_C_01.09.07P
Kernel: 2.6.32.9-g55626e1, w30471@il93lnxdroid08 #1
ERI: 5
PRL: 52105