For the thin comment; he looks tucked and light from a very finished racing career. I've never seen a thoroughbred in perfect racing condition come out without dropping.
He has nice straight legs, how thin the pasterns and the cannons on his front legs are though scare me.
He looks incredibly turned out at the knee in his nearside front.
He has a nice length of back. His shoulder is just a tad on the straight side, not a bad thing if you're interested in jumping, it'll mean for a tighter tuck at the knee's. He has horrible hip angles (atleast form the picture, it's not the greatest confo shot).
His neck ties in very high, and he has a pretty dull coat as well.
But in saying that, atleast 75% of those things I mentioned don't matter :P
I have a feeling he'd make an awesome jumper with the right training, food and rider.