I agree with you HB, but so many people are crazy litigious these days it's ridiculous.
Whatever happened to personal responsibility, and taking the blame or credit for your own actions?
I think it's a very nice thing to offer, but I'd get everything in writing. That's to cover both your and the owner's butt, because what if something happens to the horse while you're riding it? YOU may not be a litigious creep, but the owner very well could be.