This is reasonably clever, and the video is cute. Adrian in Vancouver, BC has a bicycle cable lock integrated into the seatpost. You can buy his “InterLock” cable via this Kickstarter project.
Yeah, it’s a cable lock, which is pretty useless for Santa Cruz, San Francisco and downtown San Jose, California. For suburban rides (like near my office in Santa Clara), I’ve found a cable lock is just fine for quick runs into the coffee shop, but your mileage may vary. Seatpost size is 27.2mm, which is your standard road bike seatpost diameter.
More info, including HOWTO video and pretty photos, over at The Interlock website. H/T to Grego in San Francisco, who suggests this Interlock might also be a good idea on transit.