Apparently its a "breed" but not an official one. I suppose you could consider it yet another "designer breed". Breeding any dog for size alone (ie: mini, teacups, etc) is wrong, IMO.

They DO have a registry however (that does not make them any more legit though).
http://www.mascaonline.org/
Its only about 10 years old, however.

Many breeders who breed standard Aussies also breed "miniature Aussies" I suppose so they can pass off the non-standard Aussies as "miniature" ones and still make money

History: http://members.aol.com/MiniAussie/History.htm