I'm in favor of it but it needs regulation. When I was in Paris recently I rode one around the city and it was one of my favorite experiences in the city but I was probably a nuisance to Parisians at times even if I didn't realize it...
I would love to commute this way as well but I think it needs regulation for sure. Especially for more casual tourist type users.
It's too easy to get hurt, go one one ways the wrong way, go on sidewalks etc. The rules should be clearly defined.
Article I read on the SF Chronicle today: Scooter mechanic, once homeless, says cheap rides now help him pay rent