Right. I'm sure a large number Facebook's current users have devices on their networks that are more than capable of hosting an HTTP server (and maybe already do): the aforementioned DSL/cable modems, plus wireless routers, Roku boxes, video game consoles, etc.

Also, why not just host on the home's PC? Look at what the botnets have done. No technical knowledge required, easy installation, automatic upgrades, and no maintenance for the "host" (double meaning intentional).