They are packaged for Ubuntu, technically (12.04 Precise) but you can just add the apt-repository line to your `sources.list` and it will work fine, and plenty of people are doing this.
A repository for the STABLE branch will eventually appear on http://deb.haskell.org, but I'm not sure when Joachim will do this.
GHC 7.8 is already packaged in Debian experimental, so if you're running current testing, you may find it easiest to just add sources for experimental and sid, set the default release to testing (so you don't upgrade anything else), and then install GHC 7.8 directly. You'll end up upgrading a pile of Haskell packages to versions from experimental, but mostly not the rest of your system.
The binary distributions install alongside your system packages or other bindists quite nicely (they might overwrite the /usr/bin/ghc symlink, but that's it) and you can select which ghc version you want to use when using cabal with the `-w` flag. Each will keep a separate package db, etc. So be bold!
They are packaged for Ubuntu, technically (12.04 Precise) but you can just add the apt-repository line to your `sources.list` and it will work fine, and plenty of people are doing this.
A repository for the STABLE branch will eventually appear on http://deb.haskell.org, but I'm not sure when Joachim will do this.