florinc,
Thanks for the tip on the chip! Although a "8th-order low-pass elliptic switched capacitor filter" sounds a little scary, it's definitely worth looking at. 
Re stopping the game, I didn't do a complete job, but I did 3 things:
- had a max generation count that always stopped after 50 or so generations.
- checked each generation for >0 leds to light to stop if the colony died.
- set a flag in "BirthDeath()" that indicates that cells are still being born or dieing. If the flag is not set after leaving the function it's assumed the colony is static.
Note the above does not catch an alternating static patern. That would be nice, but I got lazy. (The max gen will eventually stop it, but it would be nice not to have a max gen.)
Re: X10, I also added that. (You sure you didn't bug my basement? ) You can do it wirelessly using this: Arduino Playground - CM17A.
(Take it out of the case, remove the DB9's and use a large shrink tube or tape to make it even smaller.) You can use the IR remote or your clock to turn on lights.
Re: power, I also use a USB wall wart besides batteries. Is your idea like a screw in light fixture that powers a power adapter?
Finally, thanks for your comments on the case. I also enjoy woodworking which fits in nicely with this hobby.
John