Recent change in the overlay removed all but x86, amd64 keywords from ghc-6.6. Have been using ghc-6.6 on ppc for months without problem. Reproducible: Always
The ebuild in official tree is already keyworded ppc, so... hmmm? :)
We are working on merging the ghc and ghc-bin ebuilds into one, it'll greatly simplify things for us. The ghc you see in the overlay is the newest one, still under testing and development. The overlay is for those who want to see what we are up to. Things are much more likely to break there than in the tree. I have added ppc to dev-lang/ghc, you're welcome to try it. Also, don't post bugs about the overlay here. Instead come and see us in #gentoo-haskell @ freenode or send a mail to haskell@gentoo.org. Thanks!