Tertill is cool and all, but for a new garden, you still have to weed until the payplants are big enough to trigger "collisions". There's no magic in sensing: It just kills new growth.
Yeah, seems to assume you're going to put protectors around the 'good' plants or something at first. Still, I could see some interesting swarm behavior opportunities for the right types of plants and growth stages...
iRobot founders' new thing. Small, and undercapitalized, but promising.