You beat me to it. In addition, a warm-blooded snake would have a lot of its body in contact with the ground at any given time, and would lose a lot more heat via conduction to the ground than would a mammal that only touches the ground with its feet.
Another consideration may be the method of breathing. Mammals rely on active expansion of the rib cage and a muscular diaphragm to bring air into the lungs. This active expansion and expulsion of air is essential for their high metabolism.
Snakes and caecilians, on the other hand, have ribs that extend down the entire length of the body, and which are used in locomotion. They have no diaphragm, and don’t breath so rapidly.
It may be difficult to have the ribs serve both as part of an active breathing apparatus, and in locomotion. Rapid expansion and contraction of the chest cavity would not be compatible with the sinuous movements needed for locomotion without legs.
I think you can find a lot of legless mammals in your average pub on a Saturday night …
Interesting. But is that true of the ancestors of snakes, which were lizards, right?
I have a mammalian trouser snake.
Do you… nope, not going there in GQ! 
Lizards also lack a diaphragm, and rely on the rib muscles alone to inflate the lungs. Lizards have ribs on all the vertebrae of the trunk, unlike mammals which have ribs on only the thoracic vertebrae (which is connected with the evolution of the diaphragm).
There aren’t many situations where leglessness would be beneficial for land mammals. It’s not clear how it was an advantage for land snakes and other reptiles in the first place (although it seems unremarkable if it was originally an aquatic adaptation). Mammals limbs are more sophisticated than reptiles’s (aside from …saurs if you count them as reptiles), with generally more adaptation to specialized usage. Mammalian limbs are more closely tied to the nervous system and cardio-pulmanar system that reptiles, something that may be strongly tied to ‘warm blooded’ metabolism.
It would be unlikely circumstances that render a land mammals limbs useless, so that genetic changes that eliminate limbs would not be detrimental to a species survival are not likely to arise. Even the whales and seals adapted their limbs into fins instead of losing them (something some penquins have done to a great degree).
Also, the snake is unique among vertebrates with its repetition of ribs and vertabrae. This probably predated the atrophication of limbs. The extension and adaptation of ribs exceeds that of similar legless reptiles. This level of genetic change may had a great impact on the eventual loss of legs. It may have been competition within an adapting nervous system that rendered the legs useless initially, or the genetic structure which permitted the adaptation was unfriendly to leg genes. But this level of genetic change seems to be absent in all mammals.
Note however the prehensile tails of New World Monkeys and the phenomanal proboscis of the elephant, adaptations which have given snake like characteristics to mammal’s appendages. There are many other discreet modifications to mammals that are not found in the reptile world, much better ears, hooves, wings, manual dexterity, fur, antlers, among others.
ETA: Does anyone have cites for the number of ribs for non-snake legless reptiles?
Snakes appear to be descended from burrowing ancestors. The most primitive snakes, the blind snakes, are burrowers. Also, details of the eyes of snakes are quite different from those of other vertebrates, including lizards, as if the eyes of ancestral snakes had atrophied a great deal and then had to be partly re-evolved when they emerged on the surface again. Legless lizards are for the most part burrowing forms.
I understand that is the CW. But I don’t mind being a heretic. There’s no consistent evidence that lack of legs is advantageous to burrowing animals. So I just ask the question, looking for refuting evidence, couldn’t snakes have evolved in an aquatic enviroment?
I do realize that the eye adaptations of snakes don’t seem to conform to aquatic adaptation, but there’s no way to tell when those changes took place relative to the limb adaptations.
I was thinking this, and how fur probably wants to stay out of the dirt more than scales, but moles and shrews (and prairie dogs, rabbits, badgers, etc. etc.) don’t seem to have a problem with being intimately in contact with dirt most of the time.
I would think that one advantage of being legless, especially if you are a burrower of some sort, is that you can more easily get through crevices and small holes - especially given the leg and shoulder structure of reptiles. Their legs are always pointing out to the sides, and can’t really be kept close to the body (unless they are so small that they are basically useless). Mammals have different shoulder joints, and can have fully functional legs without much increasing their diameter. See for example ferrets and the like - which have some similarity to snakes, being long and slender predators, but they got to keep their legs.
That’s not how it works. It’s up to you to provide evidence in favor of the aquatic hypothesis, not for others to refute it.
And there are fossil forms, like Najash, that indicate that the first snakes were terrestrial burrowers, as well as the fact (which I already mentioned) that some of the most primitive families, such as the blind snakes, are burrowers. There are several lines of evidence indicating a burrowing origin for snakes; I am not aware of any evidence indicating an aquatic origin.
Actually wasn’t there prehistoric winged reptiles?
Yes, pterosaurs.
I didn’t assert that snakes had an aquatic origin. I pointed out that the questions about how the snakes ‘lost their legs’ could be explained by an aquatic origin.
There’s nothing wrong with positing alternate hypotheses. In this case, the evidence for snakes developing as burrowers is nothing more than a hypothesis of the same nature, a WAG. And attempts to verify that hypothesis have come up empty so far.
Now after that rebuttal, here’s one cite for an aquatic origin. Wikipedia also makes a similar claim in its entry on snakes.
The Tao’s Revenge: Pterosaurs were part of the …saurs exception I mentioned earlier.
What about Falcor?
Couldn’t the need for faster respiration also be a warmblooded/coldblooded thing, since warmblooded animals have to generate their own heat (and thus need to burn more fuel)?
There’s the cat-snakes of A World Out of Time.
One more issue that strikes me is another unique mammalian feature: mammaries. Mammalian females need to feed their young. On a snakelike, limbless mammal, what happens to the teats? Scraping them along the ground while the animal slithers along like a snake seems cumbersome, to say the least.