Well they are mirrors. SATA is for windows and software.
120s are in pairs in a mirror. One for photography (I shoot raw 90% of them time with old D100 and new D1X, and keep everything on there).
Other pair of 120s is for all of my audio work (again, I save everything in wave apart from final mixes I upload on the net).
iTunes library is on the SATAs.
I do want to upgrade the 120s to something like 200gigs. 120s replaced the 80s I had before (not that much more space but all 4 were free so meh).
I also have a "tiny" 40 gig I use for all of my Fianl Scartch stuff but that dosn;t count...