I am under the impression that darcs doesn't expand a path like "~foo".
For example, the following fails for me in darcs 2.7.99.1 rc1 (the
ubuntu version of darcs):
    
    $ darcs push daj@example.org:~daj/foo

even though I can `cd ~daj/foo` if I SSH in by hand.

I would request that darcs expand these paths as appropriate, so that
that would be the same as if I'd done it locally where ~ is expanded by
the shell. In this case, ~daj is /u/daj, and it works if I darcs push
daj@example.org:/u/daj/foo .

This is established semantics for SSH style remote paths and there is no 
reason to change it in any way.