Garland/Bryan:
I did the True Temper ShaftLab a few years ago, the data you get back is pretty interesting. I wouldn't agree with Bryan that the leads and lag are "quite small in absolute sense". When I did the driver test, I had a 7.2" maximum deflection in the shaft, I wouldn't call that "quite small"!
It isn't a complete picture, of course. It said I should be swinging an S400 iron and X200 wood (if I was buying Dynamic Gold) and since I have S500 irons since 1989 and I used to swing an X100 driver tipped an inch back in the steel shaft days I guess I was pretty much on the mark with my "self fit" of shaft flex. Since launch angle takes on much greater importance these days there is still a lot it won't tell you, and True Temper doesn't make any claims that it does. They only claim it will help fit you for the correct shaft flex, and if your optimal flex doesn't also optimize toe droop, you can take that into account and get the uprightness of your clubs adjusted from their static fit to take that into account.
Some people argue that shaft flex doesn't matter -- and that's true, if you are a "swinger" rather than a "hitter". If I swing a senior flex shaft I'll hit a high hook or monster push right every time, but a guy with a smooth even acceleration could hit anything from a ladies shaft to a long drive champion's XXXX shaft and produce good results.
The one thing I learned from looking at the picture of my swing (I still have the sheets, I can scan them in if anyone is curious to see what it produces) is that I and everyone else on the planet has their maximum acceleration before they reach the ball, regardless of all the "accelerate through the ball" instruction you hear. They had Shaft Lab images from a number of pros up on the wall where I was tested, and every one of them had a drop off in acceleration before impact.
I do think that the data it produces is useful enough that if you wanted to work on your swing being able to regularly get tested on this equipment to check your progress or even experiment with different swings would be at least as helpful if not more helpful than looking at videos.