<a href="http://www.xaprb.com/blog/2008/03/19/high-performance-mysql-2nd-edition-is-in-production/">According to Baron Schwarz</a> the second edition of High Performance MySQL (the first edition being written by Jeremy Zawodny and Derek Bailing, which I read twice and still often use as reference) is in production, meaning that it's written and being prepared for print.
That's good news! As a MySQL developer and DBA, I'm very interested in knowing every piece of information about how to make MySQL perform well, and as soon as I can, I'll order a copy.