Column descriptions - could they be propagated to new tables?

Since I discovered the facilities in Postgres for providing and listing
column descrptions, I have found them very useful, especially for adding a
string showing physical units to my columns. For example:

\d+ cat
Table "public.cat"
Column | Type | Modifiers | Description
-----------------+------------------+-----------+--------------
src_num | integer | |
ra | double precision | | deg
decl | double precision | | deg
radec_err | real | | arcsec
lii | double precision | | deg
bii | double precision | | deg
pn_cts | real | | counts

However if one performs a JOIN creating a new table, all these
descriptions fail to transfer. I haven't been able to find any easy way
of propagating the descriptions - would it be a useful facility to have
them propagated automatically? I would have thought that things like
units would be useful even in many scientific applications, e.g. to have
monetary columns described as dollars/pounds/euros or whatever.

--
Clive Page
Dept of Physics & Astronomy,
University of Leicester,
Leicester, LE1 7RH, U.K.