In a rather melodramatically-titled [*] post ( http://monty-says.blogspot.com/2009/12/help-keep-internet-free.html ), Monty says there is no credible alternative to MySQL.
For some of the techies I respect highly, MySQL itself has never been a credible choice, they always seem to prefer Pg. Be that as it may, EnterpriseDB has answered this sanely and unemotionally (which is a lot more than you can say for Monty!) at http://blogs.enterprisedb.com/2009/12/29/postgresql-the-credible-alternative-to-mysql/
The punch line in that post, to me, is this: "EnterpriseDB brings the same value to the Postgres community that Red Hat brings to the Linux community". I'll bet they didn't want to twist the knife by expanding on that statement ;-)
[*] I am beginning to joke that he's planning to run for office or maybe even unseat Al Gore, just based on the title of that post