niklas.broberg:
So there is a compatibility module in the new syb. Unfortunately, that won't tell you about the moves and rationale. Most of the time, you'll want Data.Data (check "ghc -e ':browse Data.Data'" or the Haddock pages, or google for "syb" in the libraries@ archives):
$ ghc-pkg find-module Data.Data c:/ghc/ghc-6.11.20081004\package.conf: base-4.0.0.0
Thanks a lot Claus and José for the info. Since all I use is the Data and Typeable classes (presumably like so many others, which I guess was the reason to keep these in base), it would obviously be better for me to avoid linking to the new syb package when I don't have to.
Perhaps people could add details about managing the syb handover to the 'upgrading' wiki page, http://haskell.org/haskellwiki/Upgrading_packages#Typical_breakages_with_GHC...