Maybe this feature is already out there. I guess you could write triggers to do some of this.
Often when designing a database I add a start_date and end_date column to the table. The start_date is when the record was created and the end_date is when the record expired. For UPDATES, I populate the end_date and INSERT a new record. This allows you to track changes though out time.
You probably want to read up on "Temporal Databases" which is what you're talking about. I believe there is a book by C.J.Date on the topic as it relates to relational DBs.
From a curiosity point of view, there apparently used to be a "time-travel" feature in (really) old versions of PG. MVCC effectively creates a new row for every update anyway, so you could "rewind" to previous transaction IDs to see the data then.
-- Richard Huxton Archonet Ltd
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