Would this be a good thing to have?  The goal here would be to make 
forensics a bit easier in the future, and also to enable users to do a 
bit of archaeology when they need to figure out exactly who did what 
when (that said, see issue891 for patch history tracking) 

When you darcs get a repository, create a file showing a time-stamp and 
the exact command you issued to fetch it, eg. darcs get --lazy foo blop

Also maybe log major repository-modifying events: pull, apply, 
obliterate.  Maybe even record with some sort of compact representation 
(start date/end date darcs record (47 patches))