> Usernames [] have had a specific character limitation for a Very Long
> Time,

Where is this restriction documented, and what exactly _is_ the
restriction?  I've been hanging around UNIX variants for long enough
that I'd've expected to have picked up on it, but I don't recall
anything of the sort.  I've seen "alphanumeric, ., _, -"; does that
include non-ASCII letters, and if so, in which charset?  (And if not,
do _you_ want to be the one who tells Søren "I'm sorry, Hels can have
username hels, but you can't have username søren, because our OS is
stuck in an English-centric view of the world? :-)

And, speaking of that limitation...where did it go?  As I reported, I
tried a control-B in a username and it passed smoke-test, at least.  Is
there something critical I didn't try that would fall over?

> Opening up spaces and $s is, IMHO, asking for trouble.

Perhaps.  But the system is already full enough of foot-pointed pistols
that I don't see much harm in one more.  Especially when, as the
message that started this off noted, there's something useful that
requires this particular one.

> At the very _least_, if you add this `feature', add a compatibility
> note to the manpage that indicates that much third party software
> assumes alphanumeric/./_/- usernames.

That sounds entirely reasonable.  You might also note that having
multiple usernames that differ only in alphabetic case is likely to
cause trouble, too.

/~\ The ASCII				der Mouse
\ / Ribbon Campaign
 X  Against HTML	       mouse@rodents.montreal.qc.ca
/ \ Email!	     7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B