I guess mostly how useful ARE they? I have no problem bundling up in a parka to ride to school, but like ... do they get okay gas mileage? Do they even USE gas? Are they easy to pick up (and thus steal?) How do you stop that from happening?
Is a used one okay? Should I take it to a mechanic to make sure its not a lemon? Do they even HAVE mechanics? What's a reasonable price? Things of that nature ....
First off, there are 2 types of scooters out there. There are smaller scooters with 50cc motors, can do roughly 30 mph and can be legally registered as mopeds. They dont require a motorcycle license or insurance.
Then there are larger scooters which can do upwards of 70 mph, have larger motors (150cc+), but require a separate motorcycle license and insurance.
Unless what you see people riding have license plates they are probabily the former. In either case they are a lot of fun to ride and can be quite practical. If you have a short commute around town, the smaller 50cc ones could be fine, but if you are looking to cruise at 40-50 mph, you will need something bigger.
Fuel economy. My older one gets me upper 50's for fuel economy. The newer ones should get you in the 60's for something with a bigger motor and in the 70's for something with a smaller one.
Weather wise the coldest I have ridden mine was down in the 40s.... but its really cold around that point. 40's arnt bad, but you essentially have a 40-50 mph wind chill to contend with. If you are hoping to ride to class in a sweatshirt then you are looking at days in the 60's.
Price wise. Vespa is just a single brand. New you are looking at around $3000 for a 50cc one that can be registered as a moped, $4000+ for something new. There are other reputable brands like Kymoco and Genuine are also very reputable brands with slightly lower price tags. Used is definitely an option. Scooter are fairly simple, so if everything appears to work fine, it probabily is fine. Yamaha and Honda also sell scootes are are brands I would definitely trust.
Theft. They weigh anywhere from 200-250 lbs which makes them pretty easy to steal. If you have a moped legal scooter, you shouldnt have an issue just parking them on a sidewalk and chaining them to whatever is around. On campus, just chain it up to a bike rack. If you have a larger one registered as a motorcycle, then you will be pretty limited to conventional parking. In which case I would just make sure your insurance covers theft. If someone were to steal mine, my insurance will cut me a check and I will find myself another one.
Mechanics. They are out there and they tend to work for scooter shops. You might be able to find some motorsports(atv and motorcycle) shops in the area that will work on them, but its hit or miss.
My biggest recommendation would be to try and find if there is a scooter shop in your area. They will carry a variety of new and used scooters and you can check out what type of options there are.
Also, anything you can buy from an auto parts store or a used car lot with a random bunch of scooters for sale is going to be a complete headache. There are a bunch of no-name brand scooters out there sold for dirt cheap that come straight from china. There are no support networks for them, parts are impossible to get, and real scooter mechanics refuse to work on them because of these issues.