Quite a few changes tonight. Added a minor section to the page about NULL on the obvious omission that you can't search for NULL using LIKE. The most major change is that i've amalgamated the page on EXPLAIN PLAN and on SQL tuning into one page now called "SQL tracing". I've also tidied the information up and elaborated further on certain points, such as DBMS_XPLAN and 10046 event analysis (with and without DBMS_MONITOR).
Observant people may also have noticed that i've removed the section on PL/SQL tuning. It was fairly obvious information (and in some ways outdated since it was written a while ago), so it went. I will repost the information on using DBMS_PROFILER and DBMS_TRACE some time, I'm going to substantially rewrite it, but for the moment, it's gone. If you still want the information that was on there, give me an email.