MC cable is usually going to be wet location rated but Reno points out an interesting thing about the connectors not being "wet". Usually when I see MC in a wet place they enter the bottom of the box so it will drain. You can always get a fight started about whether galvanized steel is more corrosion resistant than aluminum. I suppose it depends on where you are. Aluminum holds up better around salt water but PVC is the raceway of choice there.
The boxes they use on steel studs are PVC with a lip that they screw into the stud (not a nail up). The other kind have a metal bracket on the side that gets screwed into the stud, some of those now have a bonding lug that extends into the box so they can meet the Florida code.
