I don't think we should work on this right away, but it would help quite a few
people.  It seems like we would need a copy of defaultrepo's inventory, 
pristine and patches (good thing we have all that hard linking).  Seems like a
scheme where we lock the remote repository, sync, apply on our copy of the
remote repo, sync, unlock could be doable.

We'd also need to gracefully handle people pushing to different repos.

I'm just mentioning a few words here that I previously tried to use to search
for this topic (so that I am more successful next time): rsync ftp darcsless
("remote" was the successful keyword last time)