I thought you might get the western connection! That helps with me, since I started riding my gelding in western. A lot of people ride with their thumbs in. Some know the correct way and develop bad habits (like I used to).. others were never taught or taught themselves to ride. http://www.flickr.com/photos/strochka/61085214/
Take this girl, the elbow to bit connection is clearly broken. (I can't tell, but I'm assuming her thumbs are in) She needs to bend her elbows and rotate her hands so her thumbs are up. It might help with her horse's frame as well. The good thing about riding with your thumbs up, is you can better grip the reins so they don't slide through your hands (or so bad pony can't yank reins! Lol)..
(I just did a yahoo search for that image so if it belongs to anyone LMK)