MySQL vs Postgres (vs MongoDB)

Chris Travers has a fairly nifty article up titled O/R Modelling interlude: PostgeSQL vs MySQL, where-in he makes the claim

MySQL is what you get when application developers build an RDBMS.
PostgreSQL is what you get when database developers build an application development platform.

This isn't really flame-bait - its intended as a statement to show how people approach arguments (flame wars?) about MySQL vs PostgreSQL.  To paraphrase Chris,
MySQL has been massively disruptive because it tends to really, really look at the world from a Use Case perspective, answering the questions "What problem are you trying to solve", while
Postgres has been massively disruptive because it tends to look at the world from a theory perspective, answering the question "How should the database work in the solution"

I'd add MongoDB to this mix though, and extend the above quote to say

MySQL is what you get when application developers build an RDBMS.
PostgreSQL is what you get when database developers build an application development platform.
MongoDB is what you get when GUI developers build an RDBMS.

MongoDB has a great GUI, the documentation is spectacularly good, the API is pretty neat (OK, from a RoR perspective), and 10gen has great marketing, but the Design Decisions underlying the database?  Boy Howdy, are those entertaining - and not in a good way.

Global write locks, three config servers, destructive updates, and so on, and so forth - definitely fodder for late night entertainment, and once again, not in a good way.
Or, to put it differently, its like the "Booth Babes" at trade shows - they look good, suck you (ok, the guys) in, but are basically eye-candy for item actually being displayed
 
Boys and Girls, Database Theory is hard.   
Seriously hard.
Don't let anyone tell you differently.
And no, I'm not talking about using databases, I'm talking about the fun stuff associated with building databases from the ground up.
If you doubt any of this, just take a class - one of the first (literally, one of the first) things you learn is how to lock your little Database to do CRUD stuff.  And then you realize that its easy to lock the table, but locking just the row (or god forbid, the cell) - oh my, quantum jump in difficulty.
The point behind this being, this is stuff you only find out if you know the problem exists in the first place.

So yeah, MongoDB is what you get when GUI developers build an RDBMS...