Very true- if it's done correctly, it is not harmful. :) I mean jumping like 5ft on a horse who can't even jump 2ft correctly is pretty harmful. Some horses can't lift their legs up, or they don't have enough muscle. Most likely though, if you ride a horse who's a good trained jumper, there shouldn't be any problems.
Jumping is really fun. It's very nice to keep moving up on the jump size as well, it's exciting. :)