I am going to slightly disagree with you. However, I do agree withyou that the recent fashion trend of dyno'ing your bike to show your buddy is a bit annoying. Oh well, maybe Paris Hilton will do it and it won't be cool anymore.
Most inertia brake chassis dyno's are garbage, but an AC, eddy current, or water brake chassis dyno can be a very accurate tool. An engine dyno and a chassis dyno are meant to be used differently, but both are are generally very accurate is the torque absorber and instrumentation are above a certain level of sophistication.