I just discovered that 'darcs mv' does _not_ play nice with filenames containg a
plus sign (+); it consistently states "darcs failed:  There is no file or dir
named my+file.h in the repository." The whatsnew command worked fine on it,
though, and I was able to get it into the repository with no issues (presumably
with 'record -l'; I don't remember now).

This is a major problem -- if darcs refuses to work with some files, it is
useless. The '+' notation is commonly used in the filenames of Objective-C
categories. Similar issues also exist, such as issue 65 relating to 'annotate'
(submitted by me).

It has been stated many times on the mailing lists that darcs treats filenames
as byte sequences (and not, say, UTF-8). If this is the case, every command
should treat every filename equally. Or at least the same filename equally.

As a workaround, I edited the pending file myself with no ill effects (darcs
says it's consistent).

Can you give us more details?  I just tried this in Linux using the latest build
of darcs-unstable and I was unable to reproduce it.  I created a repository,
added a file named one+two, recorded, and did a mv of one+two to three, and it
all worked.

Make sure your shell isn't doing any manipulation of the filename, too.

Sorry, I cannot reproduce this either.  Please reopen this bug if you can
reproduce it with 1.0.6.

If you're under Windows, please reopen it and add the topic Windows.

Yes, this seems to be fixed as of darcs 1.0.6.