We're all built a little different, but here's my $.02
I also had 2 knee surgeries on my left knee, about a 2 yrs apart. I pretty much have no cartilage in my left knee. Most days it doesn't bother me, every now and then (when the weather's changing) it does.
Things I can't do
BOSU - OWOWOWOWOWOWOWOWOWOWOWOWOW!!!!! For days on end afterwards. The physical therapist actually gave me one of their extras. I'm glad it was free. This even hurt my good knee.
Biking - flat is good, uphill is OW.
Swimming - 1st off, I can't really swim, I'm a dog paddler
but the kicking motion in a "real" swim causes my knee to ache.
Knee pushups - it just feels weird
Low Max - causes achey knees the day after
Things I can do -
Run, jump, skip, hop, step, step, kickbox, lift heavy, yoga (yick), mambo, cha-cha, strut in my high heels, and the electric bugaloo
I'm a no-go on the BOSU.
Nan
ETA: My ortho doc told me I really shouldn't do all the impact-y stuff, but the therapist said I can do what I want as long as it doesn't bother me. I chose to listen to the PT. When I'm not active, things get achey, too.