I'm not a DBA but I am a fan of PostgreSQL. What I do hear on the PostgreSQL lists is that several of the features that MySQL gained for version 4.0 have been standard for quite awhile now. I know my own development has expanded to use much of PostgreSQL's features including triggers, rules, functions, referential integrity and views. I really appreciate PostgreSQL handling all the details of what happens when I delete a record from a table. The normal referential integrity checks then go through the other tables that reference that table and ensure that the related information is suitably cleaned up. I could do all that work in MySQL but then that just means I have to write additional perl code to implement it myself when (in my opinion) the database should be able to handle that on it's own. Others can speak to the widely known scalability issues - multiple simultaneous clients bringing MySQL to a stand-still. In general, from my non-DBA perspective PostgreSQL beats MySQL on features and scalability.

Others can speak to the variations between each on select/update/insert speed. I could (and initially did) go on about how PostgreSQL is supposed to be faster for things that aren't simple SELECT operations but... well... I was getting farther afield from my experience than I should. My perspective is that PostgreSQL is a database I can grow into - there is additional capacity for getting further into it should I need to. MySQL - well from what I hear I'd already be pushing it and frankly, I don't want to do that for data I'm responsible for. I would characterize it as a question on when you want to upgrade - do you want to upgrade to PostgreSQL now or upgrade later? I'm just doing that from the get-go.

Oh yes, I should also mention that I never considered non-free databases since my perl/RDBMS work is all for non-profits which couldn't spend money. I have no opinion on 99% of the other databases except for Lotus Domino (which rawks) which I develop for and use on a daily basis.

So... if MySQL has somehow implemented all the features I'm using in PostgreSQL then that'd be nice to hear as well. I won't switch but I'll at least learn the sucker. ;-)

Update addition: I really like Ovid's characterization of the question over at 203521. I think my response is just a specific instance of the more general question. In my case PostgreSQL has features I need so... I use it. No rocket science there.