Green IT and Motivating Users to turn off their machines

Hi All,

We're looking for a way to inform users about the on-time of their machine for the purposes of reducing our carbon world/future debt. The fledgeling of the idea is to,

1. Create an task that runs on all clients every 30 minutes that saves a heart beat to a file. Configured to execute only if the machine is on at that scheduled time.
2. Every month, have a task that runs only if someone is logged in
3. The Monthly task will take note of the heartbeat count, and if it pretty much looks like the machine is never turned off will present a widget to appraise the user of the equivalent CO2 with steps to improve should they wish to.

The reason for doing it this way (rather than enforcing across the board with group policy) is that we reckon that about 50% of the users that don't turn their machine off do so for good reasons. So, we're aiming for the other 50% who just do this perhaps out of habit.

A couple of notes,

1. The machines are initially deployed with sensible power saving settings so the 10-15% of users have their machines constanstly on have changed the deployed defaults
2. The SMP as it stands gives us an excellent indication estate uptime (using the configuration update request table), so it's not monitoring we are after. It's incentifing the user to do things better.

We're at the point of perhaps creating the little widget... but before we start that I wondered has anyone else tackled this? And if so, how?