This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
JAMon is an in memory operation and does not log anything. It can also be disabled at any time during runtime. Typically I monitor any IO (page requests, sql) with jamon, and any high level business methods that encapsulate a lot of business logic. The statistics are very useful for tracking down performance problems.