HFS+
Man its time for HFS+ to die out. What'd that debut in, OS 8.5? It has to be the only popularish filesystem that makes NTFS look good. I just hope Sun made some decent money in the deal...
Then again, is there a case-insensitive version of ZFS? I know that if you run OS X with a case-sensitive file system lots of fun issues come up. (Dreamweaver, the horrible program that it is, attempts to access its own scripts with multiple different cases, so it just totally breaks.)
I do wonder how Apple will attempt to impliment all the complex features of ZFS in a nice, friendly GUI. They'll probably just not let you get at all the fun bits... typical.