When doing darcs record after darcs replace, there's no feedback of what will
actually get replaced. This is not optimal.
I think record should print
replace ./FILE [A-Za-z_0-9] titi toto (42 occurences)
and hitting v should show where these occurences are.
This would be especially useful for files without occurences of titi, or for
occurences which are in comments.

This one might be tricky to pull off because we only display the patch contents
and not their effects on the repo.  It sounds like making this happen would
require a bit of rewriting.  Furthermore, it might be a bit misleading in that
it could make users think that only those 42 occurrences of titi get replaced,
whereas the darcs replace patch would affect any occurrences in other repositories.

Sorry for all the recent shooting down of cool ideas, Florent.  But I think we
need to wont-fix this on the grounds of it being impractical to implement (and
potentially misleading).  Feel free to prove my wrong.

(*) I'm developing a slightly more ruthless about batting away ideas to keep 
bugtracker to focus more on tasks which are either really really important or
easy to achieve (however long term they may be).  The right way to respond is
probably to continue throwing ideas at the tracker.  Some of them stick :-)