Rock Band Auto-Callibration - An Accurate Way of Measuring Video Lag?

I know this post will apply to only a small number of people who post on these forums but there's no harm in asking.

Rock Band 2 and Beatles Rock Band have an auto-callibration facility that can be used with the premium Beatles Rock Band guitars (and the Rock Band 2 Fender Strat in the U. to compensate for the video lag and audio lag inherent in AV systems. I'm wondering if anyone has an opinion of the accuracy of these systems particularly as the figures given at the end of callibration, with a bit of subtraction, should give you a number for lip-sync adjustments on AV receivers.

Having played Guitar Hero 2, Rock Band, and Rock Band 2 with wired controllers callibrated manually I must say I was very impressed with the improvement I felt when I got my Gretsch controller and auto callibrated for the first time, but are the numbers reliable?