[Nelson69]

Well, MySQL has been easier to set up, that cannot be underestimated; I've basically saved off a pair of configuration files I've just reused a dozen times to set up PostgreSQL. MySQL also works pretty fast right out of the box, if you data is smaller than physical memory, it might be nearly as fast as you can make it by default. PostgreSQL has fairly conservative performance settings when first installed, you can make it really sing but it takes some tuning and in some cases that tuning requires a fairly deep understanding of your data. Think most MySQL users are not DBAs, all the data specific settings for a PostgreSQL like database might frighten them some; it's a really odd juxtaposition when you think about it, stereotypically, geeks are drawn to the knobs and dials you can play with but I honestly think in this case it turned them away.

Then a little bit of support from ISPs and corporations and it's a no-brainer for most folks. All the oss CMS and blogs and everything support MySQL really really well. ALl the ISPs pretty much use MySQL as the "database" solution.