As an American pastime, trampolining has had its ups and downs: touted by P.E. teachers in the '60s, declared unsafe by the American Academy of Pediatrics in the '90s. Inaugurated as an Olympic event at the 2000 Games in Sydney, the activity appears once again to be on an upswing. And now trampolines are a hit not just with kids but also with exercise-conscious baby boomers and teen snowboarders. "Sports right now are aerial the higher the better," says Lani Loken-Dahle, a trampoline instructor at the University of Oregon. The aap still frowns on backyard bouncing, but nearly 700,000 trampolines were sold last year.