The MySQL Performance Blog (www.mysqlperformanceblog.com) written by the employees of Percona is a great resource for information about performance tuning or MySQL Benchmarks and is generally among the top company contributors at Planet MySQL (planetmysql.com) central blog aggregrator.
A number of employees also maintain personal blogs including Baron Schwartz (xaprb.com), Matt Yonkovit (BigDBAHead.com) and Morgan Tocker (mtocker.livejournal.com).
