Funny you should ask that right at this time. Here is a recent post from someone who got a new scooter over the internet a few weeks ago and now has what sounds like a big problem with things coming loose.
http://letsgoscootin.com/forum/viewtopic.php?t=132
On the other hand, I've put almost 3000 km now on my my 150 and have had a problem with the back wheel nut beginning to come loose(twice) until I drove it on with an air impact wrench. Also I've had the air intake hose fall off the air cleaner housing once because of a bad clamp, and had the carb begin working loose out of the intake manifold once. I checked things routinely and frequently at first, and also have found a few body panel screws coming loose now and then, and at the very first, found a number of loose electical connections... that just weren't pushed together tightly enough in the first place. That's been about the extent of it. Pretty normal, I'd say. I don't check things over as thoroughly or frequently now as I did at first, but when I read posts like the one I linked to, it reminds me to go out and check stuff over again. I do make routine checks on suspension components, brake calipers, and the exhaust system, but other than the back axle nut, haven't had problems with any of that stuff coming loose.