I used to use it for gentoo locally even, but I don't remember why and I don't think I only used it for stage1. I do remember that even locally it had a huge impact on build times.
I used it for normal package builds in Gentoo for a while but the hit ratio was not too great. Even small USE changes modify the command line (or a shared config header) for most compiler invocations in the package. Same for going from release version to release version. I think it makes more sense for development builds where the changes from commit to commit are smaller.
Oh yes. I meant: started a complete stage1-3 build. Building the compiler chain and the kernel was but a single can of paint to watch dry (among a display case of cans)
