I do this sort of thing, and I highly recommend it, especially with PG. Another thing I like to do is to use queries against the pg_* tables to generate code/metadata for components of the application running outside SQL.
Another useful thing to do is to take advantage of record types. PG SQL is approaching something that one might call higher-order SQL.
When you can query the SQL schema using SQL queries (though I admit that the pg_* tables kinda suck) and when you have things like record types, you really do have a very powerful SQL.
