I noticed, that
git annex copy --to REMOTE FILES
git annex copy --to REMOTE --not --in REMOTE FILES
behave differently. The first does not check, whether file contents are already in the remote the latter does that. I realize that this mimics "normal" (UNIX) copy behaviour but I was not entirely certain this was desired. Depending on the type of the remote and its configuration (encryption) the latter is considerably faster.
Just my two cents.