Functionality in database or external langauge

I'd like to get people's feelings about the topic.

At one extreme is to use table locking and external language queries to
even do referential integerity - a la Old (present?) MySQL/PHP.
A more realistic low end is to use Postgres or something more towards
heavy iron (if necessary) and use referential integrity, data integrity,
check cababilities.

At the other end is to only allow access to normal operation of the
database via procedures for only predefined operations on the data, with
different levels of authority in different scripts with different users.

It is a lot easier to change databases is the functionality is in the
external langauge. Both the access and the data integerity and business
rule enforcement is a lot better with only procedure access.

What's everyone's experience with these paradigms?