The need to recompile everything after upgrading was recently mentioned, I think, on this list. After upgrading from .1 to .2 (trying to get profiling on track), ghci gave me a slightly cryptic message about an unknow symbol ("stg_gc_enter_1"). No big deal, and after I removed the .o's, everything seems fine.

But perhaps ghc could tag files with its version, so that ghci (and possibly ghc when used for linking?) could be a bit more explicit?

Yes, I'm planning to do this at some point. Cheers, Simon