Not frequently, but yes. Was forced to move from Oracle to Postgres, not that I mind Postgres. Very little software changes were required to get up and running. If everything was in views or stored procedures the change would have taken months instead of weeks.
On the other hand, I had to write for some software that supported both Oracle and Postgres (many deployments, new using Postgres and old migrating over time to Postgres) and it was a chore. All tests had to be run in both, SQL was 'same but different' with different types, and for perf reasons there was tonnes of hinting, which obviously pg ignores so overall performance was very different.
