This just happened to me:

$ vim *.cabal # update version number to 0.42
$ cabal sdist
$ cabal upload dist/.....tar.gz
$ darcs tag 0.42
$ darcs w 
#darn.

Please make "darcs tag" warn if there are unrecorded changes in the
working copy.

Thanks,
Joachim

Actually, what happened to me was:

This just happened to me:

$ vim *.cabal # update version number to 0.42
$ cabal sdist
$ cabal upload dist/.....tar.gz
$ darcs tag 0.42
$ darcs push -a
$ darcs w 

...otherwise "darcs oblierate" could have helped me.