Another word from a developer
I entirely agree with Micha.
But this all depends on the application being developed. I get the impression that nearly all of the DBAs discussing the merits of one DB or another are missing the point in terms of most database driven applications developed today. That is I would estimate that at least 90% of such applications will never have a need for any specialist feature of all the big DB manufacturers because they will never experience such huge demand. I'm talking about small agencies developing small, low volume, websites for many different clients. Such clients couldn't care less about the DB. For such developers systems such as Hibernate, Ruby on Rails or Subsonic are a godsend exactly because they cut out the entire DB layer. Sure Yahoo or Amazon will never be able to run their systems using off the shelf ORM tools, but then most applications are not Yahoo or Amazon.
If you have the cash to employ a full time DBA then obviously you'd better make sure you are using the most appropriate DB. Until such a time the question is not relevant in my view. And if you run into DB optimisation issues before you can employ a full time DBA then there is something wrong with your business plan!