Anyone ever use thier Garmin features to track you mileage/driving style?

[DarbyWalters]

I just got a FREE Garmin 205W (W=widescreen) from a friend who will never use it. It has a couple of features that might be interesting.

First, you can set up your vehicle including City/Highway MPG and Cost/Gallon. It will then track your driving and give you a running tally of $cost as you go. I set it up and so far it has been pretty accurate...

Second, it has a "Driving Challenge" function that judges you on a scale of 0-100 for accelerating and braking smoothness. I haven't set that yet since I just found that feature...should be interesting.