Ok, I admitted to being a geek a long time ago, but here’s what I’m thinking:
Take Apple’s new Mac Mini, which is 2″ in height (slightly over 1U). Put several of them on a metal tray. Why? Because it can become a makeshift blade server. Granted your limited to Firewire, USB, and 10/100 Ethernet. Regardless, for rather low cost, you can get some decent power. All with 2U of rack space. IMHO that’s pretty cool. Looks like it’s a pretty simple way to get a cluster. You could even use it for some decent web hosting. 1 as a DB server, 1 or 2 as an Apache server, and perhaps a squid proxy. Mail, DNS. Each could have their own redundancy. All in 2U of rack space.
That’s amazingly low cost for having so many CPU’s, and being able to spread out your load on several physical systems.
If I had the cash, I’d give it a go.