Quite a list you wrote down.
You're absolutely right that Home Automation can help you save on energy. Although that is not my main reason to "do" Home Automation, i would rather not have Home Automation raise my energy costs even higher as they already are.
So, that's why i went looking for a "low energy PC".
My Geode intermezzo didn't completely satisfie me BTW; built a PC with that CPU, with only the basic components, resulting in a power usage of 60W. Too much(?). Costs for the components were around EUR 150.
OTOH, i have an Athlon Thunderbird 1200 here, that consumes 100W when idle..so..
Did some experiments on the Geode with some tools like s2kctl ("CPU Cooler software") which managed to bring down the power usage from 60 to 50W, but that also gave me stability issues. So, back to 60W again.
I've been looking for a cheap 2nd-hand laptop as an alternative. Around 600-800 Mhz CPU should be able to do the job (gathering all data and putting it into a Database) for me.
But i've already noticed those aren't that cheap either, and the lack of connectivity (RS-232) will become an issue in the future i think.
Further more, an older 735 MHZ Pentium 3 machine already consumes 45W. So maybe i'll just stay with the Geode and put all HA-related stuff on it.
So i'm still searching and trying...maybe, i'll end up with an eBox...who knows...