I guess it depends on where you are located and the climate there, but metal roofs are very popular here.
I have a 25+ year old metal (Galvalume Multi-Rib from Metal Mart) on my house. It is screwed to 1/4 lathe set on 12" centers. No one has walked on the roof, not even during installation, except at the ridge. It is on a 5 in 12 pitch.
My shop was built in 1974. Steel building with painted sheet metal. The only leaks in the roof are the fiberglass skylight sheets, which have deteriorated. If the leaks continue to get worse, I am going to screw a piece of sheet metal over each of them.
