It looks like a simple export DARCS_SLOPPY_LOCKS=1 solves the locks issues. I still wonder why sshfs doesn't provide this but… Well of course, it still doesn't work. Now the problem is with the following error darcs: _darcs/prefs/repos-0: renameFile: permission denied (Operation not permitted) Ooook… first I can't figure why a rename would be needed, and second why the hell would it be forbidden? My user id is correctly translated by sshfs, I can definitely mv files and touch them. Very strange. I'll have to ask #darcs, it it exists

Update: it looks like a workaround has to be activated in sshfs (the one mentioned in the FAQ as a cure when mv fails). For the record, my mount command is now the following:

sshfs user@host: mnt/point -o idmap=user -o workaround=rename