Metal transmission line posts are being used in my area at an ever-increasing frequency. Most recently, a new transmission line was built to serve the Oakdale substation for Licking Valley RECC, and all the posts are metal. Plus, Kentucky Utilities has replaced some older poles/posts on the transmission line between Richmond and Beattyville with metal ones.
I haven't seen a metal distribution line pole, however, other than in places where transmission and distribution lines share the same posts.