From a Reason magazine perspective, it seems to me that a Bloomberg Administration is likely to be substantially more libertarian than either a Democratic or a Republican one would be. Bloomberg, however, is specifically identified with a brand of trivial nanny-stating -- indoor smoking ban, trans fat ban -- that seems to be to aggravate libertarians in a manner that's out of proportion to the actual significance of the policy issues.
In defense of the Bloomberg haters, he is "specifically identified" with trivial nanny-stating because it's the main thing he's known for on the national stage and he does tend to take it too far, even by the standards of many people who don't mind a little gov't meddling. Libertarians aren't reflexively rejecting any candidate who engages in a little nanny statism - Bill Richardson is a smoking ban supporter (not to mention a cock-fight ban supporter), but they're not exactly calling for his blood.
On the other hand, I don't think I'd be risking my libertarian cred too much to say that Bloomberg may accomplish the small feat of being the most libertarian-friendly presidential candidate coming out of New York this election.