Yup, I love it when other people get on my horse.
I let this 10 year old girl who was about 4'8, or well, really really short, on my 17.3 hand gelding and she jumped him 2'6-2'9 fences! Also, my trainers encourage us to switch horses in a lesson, or even switch horses in a senior class at a AQHA show just so we can get used to riding other horses, if we want to go on an equestrian team for college! Also, my horse is broke to the point where it doesn't matter who rides him, he knows his job and will tell you when your doing something he doesn't like or if your doing something wrong. He's such a good boy(: