My wife and I (she's 140 lbs, I'm 185) have been riding our 2007 People S50 4t two-up for going on three years now with no problems. It's a little slower getting to max speed (about 35mpg) with two of us, but it gets there, even on moderate hills. The scooter is stock except for being derestricted. The scooter just turned 6,000 miles and we've had no problems, even here in South Texas where most of the year it's hot and in the summer, it's _extremely_ hot. Many of our rides have been more than an hour long at full throttle. The scooter doesn't seem to mind a bit.
By the way, I've been riding motorcycles for nearly 30 years and currently own and ride a 1972 CB 750 and a 1994 Honda ST1100. I'm quickly becoming a convert to scooters though.