I’ve often wondered why people seem to prefer either MySQL or PostgreSQL. For the most part, I think it comes down to the following:
* Familiarity.
* Friends (a.k.a. support system) being more familiar with one over the other.
* Ease of getting started. Most web hosting providers support MySQL out-of-the box.
* Name recognition.
* Ease of support.
Here are some resources that could be useful for learning the pros and cons of each database:
* [What MySQL can learn from PostgreSQL](http://www.scribd.com/doc/2575733/The-future-of-MySQL-The-Project)
* [What can PostgreSQL learn from MySQL](http://www.postgresonline.com/journal/index.php?/archives/48-What-can-PostgreSQL-learn-from-MySQL.html) and the [accompanying presentation](http://www.commandprompt.com/files/mysql_learn.pdf)
* [MySQL quirks and limitations](http://use.perl.org/~Smylers/journal/34246)
* [Why PostgreSQL?](http://wiki.postgresql.org/wiki/Why_PostgreSQL_Instead_of_MySQL:_Comparing_Reliability_and_Speed_in_2007)