table creation/modification datestamp

As a DBA, it would be extremely useful to know when tables have been
created or modified.  PostgreSQL doesn't keep track of this, does it?

(Table modification, in my mind, includes INSERTs, DELETEs, UPDATEs, and
changes performed via ALTER TABLE.  It does not include physical changes
that may occur on the table due to VAACUMing or CLUSTERing.)

Obviously, I can't use the relfilenode attribute in pg_class to check
for table modification and look up the file's timestamp, since the OS
updates the timestamp whenever physical changes occur.  Further, I don't
think linux even tracks a file's creation timestamp.

The stats collector already tracks when a table was last ANALYZED, it
would be nice to expand this functionality to include table
creation/modification times. (Ideally, table timestamp record keeping
should be persistent over db dumps and restores.)

Cheers,
Kevin