I first encountered AirBed and Breakfast at Connecting '07. It was formed out a need because the local hotels were getting packed, so the team took advantage of the opportunity and created something fantastic. Now they've expanded it so that anyone can set up an AirBed and Breakfast for other summits and conferences. Their site does a wonderful job of telling their story and how it works, I highly recommend it looking it to see both what they offer, and how to tell your story well.
[image via surf europe mag]
There is a similar project going on over at CouchSurfing.com [thanks Audrey]. A little bit overwhelming compared to AirBed and Breakfast, though its on a much larger scale, over 35,000 cities and 450,000 people! This social experiment is an interesting use of space combined with decentralizing "the hotel" by centralizing it in an online network. This won't replace hotels for various reasons, I imagine it creates richer experiences though.