>>20
Because PostgreSQL doesn't have some of the features I wanted to use, such as consistent snapshot transactions or the four isolation levels (implements only two, and if I understood correctly serializable is daring on locks), and because its replication capabilities leave a lot to be desired (or so I've heard from people who have used both). Another reason would be the ability to switch from InnoDB to the solidDB engine for MySQL, which is supposed to be pretty darn fast (and GPL as well).
MySQL is not that bad. It has a terrible image in some circles such as /prog, part deserved (e.g. the stored procedure language is utter shit; I wanted the forced indentation of code like PostgreSQL has), and part due to its past failures (such as not supporting transactions or referential integrity, and dissing these features in the docs). However, that was before version 3.22, and now it's about to release version 5.1. A lot has changed and got better and faster.