That being said what are your experiences and how do you deal with the situation?
My rules of thumb for such events are:
1 - Get off the beast (it's time for a break anyway, right?)
2 - Get away from high ground and wide open places - You don't want to be the tallest nearby feature (or near it)
3 - Various guides (And so do I here) tell you to get at least 15 feet from other people and livestock. To prevent a nearby lightning strike from hitting more than one person. I have issues with the logistics of this;
A - No way that I'm going to let go control of my horse. How many horses will stand ground tied in the midst of thunder, lightning, pelting rain, etc. ?
B - I don't want to try to hold the horse in case it should freak. I could get hurt and that is not in the game plan.
So I generally tie my horse to a tree and recognize that it's not the safest for the horse (The tree is tall (and therefore a more prominent feature and the horses' shoes are steel and theoretically a better conductor) but is the better bet for me.
4 - I then hang out and worry about myself and the horse till the storm passes.
Of course I do try to mitigate the chances of all the problems of the above by keeping an eye on the weather forecast and knowing how to read natural weather indicators.
There you have my two cents! Hope this helps, looking forward to hearing other thoughts and opinions.