Skywise wrote:

My understanding is that of those four listed, only the
IRS has a legal right to the number.

that was my understanding too, but it seems that the
DMV can indeed require it, at least here in California
(I can dig it up if you'd like, it's probably buried in
my privacy related doc);

oh I forgot another bunch of folks who demand (and
use rather casually SSN#): anything to do with the
military it seems whether directly or indirectly (e.g.,
you wont be able to register for a high altitude training
without it, the CAP for some reason demand it, etc.)

--Sylvain