Hadoop is a distributed computing platform / filesystem. It provides HDFS which is similar to GFS (Google Filesystem) and MapReduce which splits programming tasks into small chunks. It's target is 10'000 node clusters.
March 2004 - A general, overview level guide to optimising your WordPress hosting. Covers caching, MySQL, PHP and apache optimisation in general terms.
April 2007 - A guide to optimising your WordPress hosting environtment focusing on PHP, MySQL optimisations and plugin / caching optimisation.