Advice on Multiple GHC installations

[Bradford Larsen]

I would like to have several versions of ghc installed simultaneously,
on the handful of Ubuntu systems I work on.  In the past, I have had
just a single version of ghc installed on each system, usually the
most recent stable generic Linux binary installation.

Three questions:
  1.  Does there exist an `experimental' apt repository for Ubuntu
anywhere which packages versions of ghc more recent than 6.8?
  2.  If I cannot install multiple ghc versions from a different apt
repository, does anyone have advice for how to work with multiple
simultaneous installations?  A how-to guide or anything like that?
  3.  Does having multiple installations break cabal at all?  I'd like
to be able to use ghc 6.12.* by default, but be able to selectively
choose an older toolchain for compatibility purposes, bug hunting,
etc.

Thanks!

Sincerely,
Brad