A not-quite-long-enough time ago, in an alternate reality not-quite-far-enough away, I was a career line officer. That is, I was in the chain of command, not a lawyer or some such who is not in the chain of command. I commanded squadrons and squadron sections (think "battalion" and "brigade headquarters company" if all you know is Army units—it's close enough for government work) ranging from 200 personnel on up. Most of the time, these were logistics units, which meant they were extremely officer-light. One unit had 1076 enlisted and ten officers (including me); another had 267 enlisted and two officers (including me). Thus, unlike a lot of arm-chair strategists and "force shapers," I got to see both the good and the bad of the "volunteer military" on a daily basis. (Aside: I served a lot of time in joint—that is, multiservice—units, so I'm not referring just to the USAF.)
In my judgment, a draft anything like that used the last time around would not be in the best interest of military preparedness. With the steadily lengthening training requirements to use, maintain, supply, and support ever-more-sophisticated weapons, communications systems, and other hardware, a four-year enlistment is the bare minimum to achieve "combat readiness." Consider that there are several USAF specialties—always critically undermanned during my career, and I have no reason to think things have improved—in which an individual doesn't even emerge from the basic schools for nearly two years, which is then followed by at least fifteen months of closely supervised on-the-job training before that individual would be allowed to work alone on even the simplest systems. For some aircraft, an airman could not even be sent to the maintenance unit until reaching NCO status as a sergeant (E-4)! For obvious reasons, these positions cannot be filled with draftees—and they can't be kept all that far from the combat zone, either, so "contracting them out" won't work.
So, then, what about a draft just for the cannon fodder Army footsoldiers? Although the length of training isn't as long as I've described above, one can't shove them through basic training, then the basic infantry school, and end up with a survivable soldier. It takes quite a bit more than that in a twenty-first-century military. And then there's the issue of whether we want resentful draftees on the offensive on foreign soil. There's an aphorism that "no conscripted army ever won a war" (OK, it's not entirely accurate; it's closer to "almost no conscripted army ever won a war against a nonconscripted enemy," and even that's still an overstatement) that bears some consideration here. It's one thing to call up a draft in response to a specific military need for defense; it's another entirely to take those draftees and put them in somebody else's country. And if you think that the reports percolating back of war crimes committed by US personnel in Iraq and Afghanistan are disquieting (if you don't, you're probably not reading this blawg anyway, unless you're just here to snipe), just wait until you see what happens when you give draftees guns and put them somewhere they can't find on a map or pronounce, let alone want to be.
As a commanding officer, I'd rather be below strength—even significantly below strength—with people who at least volunteered in the first place than be at full strength by way of conscription. We would be far better off rethinking how our forces are structured and employed, rather than just trying to find a sufficiently large pool to continue with business as usual.