Mailing lists and IRC

GHC developers hang out on the  ghc-devs mailing list.

There is also  ghc-tickets, which receives a copy of traffic from the bug tracker,  ghc-commits, which receives a copy of all commit messages, and  ghc-builds, which receives reports from the automatic nightly builds.

The traffic levels vary quite a bit depending on how much activity there is.

IRC

GHC developers also hang out on #ghc channel on  FreeNode. This is a good place to ask questions related to working on GHC itself; if you have more general questions then #haskell is probably more appropriate.