Postmaster crashes periodically

Probably once per week or so I get a message like:

Server process (pid 12243) exited with status 11 at Tue Oct 10 01:20:01
2000
Terminating any active server processes...

Followed by one of these for each backend:

NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend died
abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am going to
terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.

I'd be interested in any hints as to how to track this down since I can't
seem to find any core files etc. This is under Linux 2.2.10 & PG 7.0.2. I'm
tempted to start using one postmaster per database (with different ports)
just so I can insulate each database from the others and see if there is a
specific database causing the problem.

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