What are your thoughts and the database of your choice?
http://tweakers.net/reviews/657/5 http://tweakers.net/reviews/657/6
Also, for their MySQL test procedures, I could not find any information regarding which storage engine they were using. InnoDB is fully ACID-compliant, whereas MyISAM has reduced overhead since it does support transactions and foreign key constraints, for example. I found a good article, http://www.mysqlperformanceblog.com/2007/01/08/innodb-vs-myisam-vs-falcon-benchmarks-part-1/ , comparing the two storage engines, and the results were pretty surprising to me.
It ultimately comes down to your individual usage patterns. Using a database abstraction layer will allow you to test your application against different databases so you can see how your application performs first hand.