Here's a podcast episode from Robert Rickover. It just dropped into my RSS reader and sounded potentially interesting:

Jo Ann Widner, an Alexander Technique teacher in Richmond, Virginia, talks with Robert Rickover about ways in which horses can be enlisted to teach you how to improve your balance and coordination. Jo Ann's website: jowidner.com Robert Rickover teaches in Nebraska and Toronto, Canada. ...
What horses can teach us about balance and coordination

I haven't listened to it yet, but thought it worth posting before stopping to do so -- Rickover is very experienced and his interviews are usually good.

Horse-riding can be good for posture: because you have to balance there's a tendency for the spine to uncurl naturally so that people sit up but without holding (i.e. not doing so by unhelpful tension) -- which is what people usually do when given the unhelpful instruction to "sit up straight".

Riding has long been realised to be of benefit, helping people to let go where they shouldn't be holding and at the same time to develop appropriate muscle-tone where it may be lacking. Hence in the UK there is an association for using it therapeutically: Riding for the Disabled:

Riding for the Disabled Association (RDA)