Hi,
after questioning the enterprise readiness ratings of MySQL and Postgres
on eosdirectory.com, they published an article about how they come up
with their rating. See here and comment:
http://www.eosdirectory.com/blogs/2009/06/25/is-mysql-better-than-postgresql-a-debate-on-enterprise-readiness/
I personally find popularity (AKA adoption in the market) way overrated
in there, but well...
Regards
Markus Wanner