I am seeing a lot more scooters on the roads around here. I considered it for my commute, but ran the numbers and don't see a pay off. In my case, the commute is 7.5 miles one way, 15 a day. I assumed I could commute on the scooter 90 days a year (good weather, a big assumption), scooter cost of $1000, and gas cost of 5.00/gallon, and 100 mpg for the scooter. Even at a 20 mpg for my car (I get around 23), it takes 3.7 years to save the cost of the scooter in saved gas. Doesn't seem worth it for me.
Different assumptions will give different results. YMMV.