conversion security update may have slowed our system?

Dear Gurus,

I dunno if it should go to -perform or -bugs, so stay with the original message.

As Tom wrote in
http://archives.postgresql.org/pgsql-announce/2005-05/msg00001.php as well
as at http://www.postgresql.org/about/news.315, I patched all our testing
(7.4.6) and production databases (7.3.3) on Thursday.

According to user reports, the production server slowed down noticeably on
Friday and is almost unbearably slow today (Monday). My humble question is,
could you think of any way this patch could affect overall speed, or is it
just a fatal coincidence?

System: Debian "Woody" @ DualXeon 2.4 1G 5x10krpm scsi hw raid 5 IBM server
Kernel 2.4.30 (patched on Tuesday, 3 days before first syndroms

TESTS:
1. As far as we could test without modifying the prod.db (i.e. issuing
updates/inserts), this server makes both simple (select *) and joined
queries in about twice the time of an Athlon 2k server on 7.4. VACUUM FULL
VERBOSE ANALYZE and ANALYZE in itself did not help.

2. Set up another database, to see if it's in-db issue, but it made no
difference.

3. Set up another database, based on a pre-patch dump (but I think it's
irrelevant since I also patched template0, but it made no difference.

Any ideas?
Since I haven't checked it before, could you please provide an "undo" for a
7.3.3 database? (I assume it's a similar update, but don't know the original
ACL values)

Yours,
--
G.