One of the most useful things I've found regarding MySQL is the deployment presentations that various sites have put together. Sites like Flickr, LiveJournal, Mixi, Wikipedia and others have put together presentations detailing their load, environments and configurations. Here is a list of the presentations I have found:
http://www.dev411.com/blog/2006/10/05/mysql-deployment-presentationsI think presentations like these make people more confident about choosing and scaling with MySQL. Is there anything like these for high traffic/load sites for PostgreSQL?
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John Wang
http://www.dev411.com/blog/