Back in the mid-90's Larry Tooke mentioned to me -- in fact he was thinking about doing his Master on the topic -- that you could run a LAN via the electricity cabling that was already in place in your house/office/school. That's now been commercialised (HomePlug for example) and I guess largely redundant now that short distance wireless technologies are so cheap.
Slashdot ran a story last week about an alternative mobile phone network that works by the phones communicating directly with each other via Bluetooth or WiFi. The network is based on ephemeral connections depending on proximity of available devices. See more here and here.
But that's nothing compared to the idea of Human Area Networks! That is, data communication via human touch. RedTacton has prototypes (in fact they've had something working since 2005) that use the body's natural electric field to transmit data. You'd have a card-sized device in your pocket (I think with a wire touching your skin) and if you shook hands with another person similarly attired, the devices can talk to each other through the skin! Or it might be that you touch a doorknob that's wired to a computer and your pocket device tells the room's computer who you are.