I just did a "man xset" and the units are very clearly there.  Of course,
I've got XFree86-4.0.2 installed from rawhide, so it is entirely possible
that the manpage has been updated since the version you're using.  I'd
normally say "upgrade to rawhide", but upgrading just to get a new manual
for something you probably know already is likely not too feasible.  ;o)

How about this:  Upgrade to Rawhide as it is supremely eye popping, and mind
blowing!  Hmm.. sounds too much like a Creative Labs magazine ad...  ;o)