Think I'm crazy? Well, I'm not the only one thinking about this. Take for example SeaMicro and their SM10000 High Density, Low Power Server. It uses ¼ the power and takes ¼ the space of today's best in class volume server. It is designed to replace 40 1 RU servers and integrates 512 independent ultra low power Atom processors, top rack switching, load balancing, and server management in a single 10 RU system at about $150k. Do that math, it basically replaces 40 traditional servers at nearly 1/8th the price per computing unit. Although there is one problem, the Atom processor which support Intel VT is 32 bit greatly limiting it's usefulness.
That's where the Laptop comes in. Let's take your lowest end laptop (Non Atom) with the Intel i3 processor. A quick search and I discovered that these laptops sell for about $350. Keep in mind these laptops come with a keyboard, and screen which add to the costs. Boil it down to just the components you need and you're looking at about $150 retail for the parts. (dual core i3 2.26ghz, 4GB ram, 500GB, network card, and 6 Cell battery)
So now consider putting this into a small form factor "laptop blade chasis" lets say a 2u or 4u size. My estimate is you could probably fit about 5 of these lapblades in a 2u or about 10 in a 4u. So doing the math on 4u (10 lapblades, 20 cores, 40GB Ram, 5,000GB of onboard storage and 10 batteries for about $1500 - $2000 net) Those same 20 cores would cost you about $25k-30k with traditional servers. So the ROI for a service provider would be days. Not to mention with ten 6 cell batteries, you've got an onboard UPS and laptops are inherently low power.
Crazy idea? Someone should do it, I'd buy one.