I used to hang out on the Stellaspeed forums a lot - and those two are the only examples I know of. If I was goign to do it I'd go with the side mount - seems more secure, and can be used to carry other things as well.
The side rack looks like the way to go for a scooter. It won't mess up the weight balance as much as a rear mounted on would. I've used the rear method on a couple of motorcycles and they worked fine but a scooter is so much lighter I would be worried about lightening the front end up too much.