When using arc patch && arc commit for a change that was authored by someone else the authorship information is completely lost.
I know SVN can't deal with this properly so you'll never fix e.g. svn blame output. However, it would help immensely if the original author was part of the commit message generated by arc.
For example I would love if the commit message contained a field like this (akin to Reviewed By, possibly only if the author isn't the committer):
Authored By: xxx