Personally I havent found cork (depending on the grade) to be all that functional for holding a pin, and the hollow door can some times be tough to push a pin in unless you use a tool, and then when removing the pin from your work it may ruin an hour or more's worth of loving labor.

I like using just plain old 5/8" dry wall board eventually it will warp, but by the time it's even noticeable it's time to change it anyway because it's been so cut up and rough from dried glue it's time to change it anyway. and it costs only 4-$5. I have used dry wall for close to ten years and only replaced it once, that was when I lived in Washington.