Automatic auditing suggestion

In my further discussion with Andrew offline, we came up with a joint
suggestion to have PostgreSQL do automatic auditing.  This would be VERY
NICE, imho.  Any input?

Scott wrote:
> It seems like it would be nice if you could flip a toggle on a
> table and have it automatically build audit entries in another table.

Andrew replied:
> Yeah - that would be a great feature - automatic auditing...
> Maybe you should post that to someone (whoever it would be?) at
> PostgreSQL - sure, there would be major performance hit problems (maybe
> rather than at table level, field/column level would be better), but it
> would be a boon for many...