Java Testing and Design - 2.3 Web-Enabled Application Measurement Tools

The best measurements of health for a web application include:

1. meantime between failures in seconds
2. amount of time, in seconds, for each user session, sometimes knows as a transaction
3. application availability and peak usage periods
4. which media elements are most used (HTML, Flash, JavaScript, etc.)

Developing criteria based on these elements is difficult but author promises to offer help in upcoming sections.  One question I had when I read this section is how to accurately determine what a failure is?  If you are trolling through server logs looking for error messages, you are likely to find lots of them.  What do I have to do in my application to make it easier to identify a real problem from a benign one?