True but think about what load actually means, you would need to run them both doing similar tasks to compare power consumption, while I have no doubt the Atom would come out on top (or is that below) it will not be as anywhere as versatile especially when it come to playing back HD content (an Atom can just not do it the ageing chipset cripples it).
Oh and my system with an Atom board and standard DVD (no point in bluray with an atom) would come in at ~£275 making the shuttle a bit expensive, you could even get a smaller and better looking case and still be cheaper than the shuttle (
http://linitx.com/viewproduct.php?prodid=12042) puts the price just at ~£310