The purchases are tied to the account and as long as the machine is authorized to that account you can download it on any machine that can use that account.I have bought Mountain Lion, but from an account on a Hackintosh.
Then I had issues with that system, I trashed and reinstalled with new disks, and since then I've never been able to get my MountainLion purchase back again ;(
I have the view/feeling that the download/purchase is linked you machine's serial/UUID number(s), and since a hackintosh's serial number is a file in /Extras, you need to copy that to the next/re-installation to "keep" your MountainLion purchase.
thought i had a common setup (ga-z68x-ud3h-b3, core i5 2500, 6870 gfx), but haven't seen anyone post on this thread with that setup saying if it worked or not.
also: i always forget which audio to repatch in multibeast after updating. is there a way to find out which one you have?