I know what pimpl is - I relearn it before every job change for interviews. But I've never seen it in use, and don't see a use for it. Compile times are rarely an issue in my experience. At least not big enough to warrant something that extreme.

I like to see things simple: I need something, so I include something. Compile times are really orthogonal to that, and mostly a job for compiler devs, hardware people, modules or whatever. Changing my code because of compile times seems pretty harsh