A friend of mine Dave Cline just sent me a link to EnOcean. 
This is a very impressive company that is leading the wave of the
future when it come to distributed sensor networks.  They have
addressed some of the key elements of a successful solution:

• No Batteries – the sensors create energy from their environment
• Wireless Communications – they sense and send their data
• Mesh Networking – they use a hierarchical mesh networking system

This is some very impressive work, and ought to get people thinking about what is going to be possible soon.