When you have a ~/.darcs/author with more than one entry, and
record a patch in some repo, Darcs lets you select in one of them and 
then stores this author in the repo as _darcs/prefs/author. It does warn 
you about what it is going to do. However, there is no way to tell Darcs 
to use the selected author this time, but NOT store it in the repo. This 
is bad in cases where the repo in question is also used by other users 
on the same host: when they record something, it gets the wrong author.

One solution would be to split the single prompt into two subsequent 
ones: one for selecting the author and a second prompt for whether to 
store this author inside the repo.