I'll risk being pounded for posting a commercial site but found this very interesting...being able to monitor your home online at a reasonable cost....http://welserver.com/index.htm
I suppose if you're obsessive enough and you have nothing better to do with your time, you can monitor every panny you're spending on energy. I'm not ready for that, not yet.
I have looked at the WEL and it is a great idea if all you want to do is monitor On/Off status and temperature of devices or loop points. However, it provides no ability to control any of the HVAC components which is what I would like to have someday.
If you Google "Rabbit Computer", you will find the website of ZCore that makes the microprocessor used in the WEL. There is also 3rd party software available called MicroCommander by Intec that provides a high level language for programming the Rabbit processor. That might be of interest for those who want to both monitor & control their HVAC system. I see myself headed in that direction in the long run.
As energy costs continue to rise, I see a big need to have dynamic HVAC contollers to squeeze out the most of evey penny of energy.