http://userlinux.com/white_paper.html
Check this out. They chose GNOME instead of KDE because Qt requires a
proprietary license for commercial apps while GTK+ is fully GNU. As they
put it the licensing "is the sole reason for this decision".
But when it comes to databases they've chosen "MySQL with non-GPL
libraries". How's this different from Qt vs GTK+?
However he does say he is "not a database pro, and will listen to
argument about the merits of other database servers". So perhaps
PostgreSQL advocacy team has something to say here.
Kaarel