Hi,
The (me)duino sounds like great fun!
If you are looking to build to a low power spec, I can definitely recommend this power saving tutorial by Nick Gammon.
http://www.gammon.com.au/forum/?id=11497]http://www.gammon.com.au/forum/?id=11497[/url]
I got my board to use sleep and interrupts, voltage at 3.7v from lipo and current during sleep < 6uA, from using the tutorial. I set fuses to disable brown-out detection and use internal 8MHZ osc. ADC disabled during sleep.
Cheers