Many people are afraid to make code changes out of fear that they will break the code. To ensure you can safely make code changes you should change it often. I'm not talking about pointless changes but solid improvements. Run FindBugs against your code and fix the issues. If you disagree with FindBugs then use PMD or any static analysis tool. However, if static analysis suggests that your code looks like a bug then consider changing it to look less dangerous.
Anyway, the point of merciless refactoring is to always be improving your code. To make changes and ensure that it was easy to make those changes. If it isn't fast and easy then you need to make changes to make it fast and easy. Write unit tests, delete unused code, optimize loops, automate tests; everything you can do to make it possible to complete your next project in record time.
Merciless refactoring can also be described as following the boy scouts rule of always leaving a place cleaner than when you found it. If you add a method to a class then add some JavaDocs to the other methods while you're there. If you change a single line of code in a method, take a look at the entire class and fix it up if you can.
