These 'thermal batteries' are also great if you live in area that experiences power outages: If you have enough insulation and a big enough volume of water you can actually go for days without dropping more than a few degrees. Not really something we want to do with our precious little balls, but a good idea if you are going to be away from home for awhile and you lose power.
I've been thinking about something similar for when I finally buy my own place and have my dedicated snake room....we'll see, but I know of a guy a few hours from me who lost his whole collection while he was away and lost power for a few days.
http://www.edmontonreptiles.com/foru...ead.php?t=1622