Considering how close it really comes to a torque-based power meter in so many conditions, it seems like it would do a fine job of tallying up rolling resistance and air drag during a test. We all know it's crap power for many conditions, but I think it would be fine on a relatively regular course, out and back, then average the readings. The thing is that, while it may suck for true power, it's a truly amazing little device with some great software on board for reading the environment around you while you ride.

I read an article on it a while back and it sounded like it was w/in a couple % on CdA calculation vs. a wind tunnel. Even with that error, all you need is relative comparison to various positions and equipment.