I've used PostgreSQL for years for my personal projects, and I usually find a PostgreSQL driver for most other DB-backed systems.
There are a few, though, that seem to only have drivers for MySQL -- MythTV and Bugzilla are two examples. I also occasionally have someone want to host a MySQL application on my servers.
To date, my experience has been that MySQL is a memory hog, I can barely find my way around when I try to just jump into using it, and I have no idea how to backup and restore the thing. It just doesn't feel safe for me to administer yet.
I'd really like to look at Bugzilla, and I really will care about that data, so I guess I must bite the bullet and learn to get around MySQL. The funny thing is that I don't actually ever write any applications to directly use PostgreSQL anymore -- all my applications are Java talking to PostgreSQL through EJB 2.1 or EJB 3 persistence APIs, so I could mostly just swap out PostgreSQL in favor of MySQL and really not care. I just really prefer that PostgreSQL came from a more academic and feature-driven development model over the years.