The Tivo of your life: CamWear
Found on NooFace: wear a little camera and with a touch of a button, save the previous 30 seconds (audio+video) to a memory card (in mpeg4).
The most expensive model allows up to 4 hours recordings.
Check it out on DejaView's site (in the products section).
The camera (320x240pixels, 24bits) seems a bit large, but the main unit seems reasonnably small (like a cellphone) and has USB connectivity.
Update: CamWear is getting closer to shipping, as a camera manufacturer signs the deal.
Update: Some reflections on how such small cameras can be used to provide distributed recording of events (like riots) to prove how things occured and discussions on the social changes that these "SnitchCams" could create.