I was under the impression that MacOSX is run on HFS..
It does afaik. But it is journalled.

Fresh on the heels of its "Jaguar" release of Mac OS X 10.2, Apple Computer Inc. is about to spring a new surprise for the Unix-based OS: A journaled file system designed to provide corporate Mac sites with a new, historical view of their data.
Taken from this article: http://www.eweek.com/article2/0,3959,634711,00.asp