Yeah, the breed standard for Munckin (TICA) specifies that they are not to have any other features that are common in other breeds, such as short noses, wedge heads, and so on. They are supposed to look like short-legged moggies, and from what I've read, it's encouraged that breeders mix them with healthy moggies for that reason.
There's no evidence of back problems due to the difference in cat spines from, say, dog spines. Cat spines are naturally more flexible (as anyone here can attest!) so arthritis or bones fusing together doesn't seem to be a problem for the breed. Rarely, some do have a "conical chest," which is actually the same condition as present in people, but if it's going to be a problem for the kitten they usually pass away before they'd even be old enough to be away from their mom. They have fewer health problems than Scottish Folds.
Some aren't as good at jumping, but remember that jumping really comes from the leg muscles, not the leg length. So while they may not be able to climb the door jamb, they can definitely be sproingy cats. I would definitely advise that you go with a responsible breeder, though, to ensure that they're outcrossing their munchkins enough to make sure they're healthy. There are some people who are mixing them with rex cats and other breeds in order to make them very, very small, which I disagree with, so choose your breeder carefully if you do go with a munchkin.