Out here in Orange County, CA, I try to use nothing but PVC underground. Not only is the soil super acidic (especially near the ocean), but alot of the irrigation systems are run with reclaimed water - metal of any kind doesn't stand a chance. I've even run across rubberized-rigid that corroded right inside the rubber from a leak at one of the joints, and just disolved into oblivion.
Concrete-encased PVC is nice, as it's basically just a plastic-lined concrete conduit. I've seen this in the snack bars that are actuall ON the beach. Works great until a plumber comes along with a concrete saw... Gotta love plumbers, they keep my bills paid =)