What Jim said plus:
Clam shells are knee and shin killers when you crawl across them to get in/out. AND they are thigh, crotch, abdomen (depending on your height) killers if you run into them. AND the cables are can inflict injury if you are not careful as well.
Other than that, clam shells are great!
Barn doors come up on ebay from time to time, and for some reason, a few people haven't actually tried clam shell doors and pay big bucks for them on ebay.
I have switch to barn doors on two suburbans, it is an easy swap.
