[wylee]

> I wonder how often it actually comes into play

I've wondered the same thing in the past, but just recently I converted two Django projects at work from MySQL to PostgreSQL. The transition was pretty much seamless--I didn't have to change any application code.

One of the projects was converted to add spatial capabilities via PostGIS. The other was converted due to an issue with how MySQL stores data (it ended up being easier in a time crunch to dump and reload into PostgreSQL than fix the issue with MySQL).