All my trips through they funneled the guests getting off the ride into a small line between an employee and a bin. The employee was watching each and every guest and made sure they "chucked" them into the bin. I never saw an employee in that position take their eye off guests for a second.
Personally, I didn't think they were noticeably heavier. One of the pairs I grabbed seemed to have some marks on the lenses, but when I put them on it wasn't noticeable.