I've been using PostgreSQL for some time with my software projects (C++ / VB / C#). This change was mostly because on some Windows systems MySQL didn't play nicely with the antivirus (temp files were being blocked). Postgres solved this problem...
On the web I still use MySQL. As I see it, there is no need for me to kill myself trying to change every website out there I'm responsible for because even if Sun or whoever it is does something strange with MySQL, they really can't prevent me from continuing to use the current version on my servers, which are are working fine as it. So, if I need some new feature in the future that is not in the current MySQL, then I will change those sites, but it really will be on a case by case basis