Well, I only started working on sited with a db recently. I jumped into mysql first, because at the beginning you are unsure of what you're getting into, and a large user base, loads of web info, and so on, has a strong attraction from that position. That is perfectly logical.

Now, after a few months, I see the possibilities of Posgres - but will I be limited enough by mySql to change at some point? Maybe, if I go for a big teardown/rebuild, which may happen. But it won't be for a while.

For many in my situation, it would be never.