There are some good nuggets in this article, but he seems to miss a point that I feel is very important and yet is often overlooked in real-world web load testing; emulating an actual client behaviour under different real-world scenarios. Hitting a page or pages X times usually bears almost no resemblance to how a real-world application is used and therefore gives no indication of actual performance and capacity.

To test a web app properly you need the ability to script and/or replay real-world session browsing behaviours, simulating typical interactions. This can be both very time consuming and difficult to set up but yields far more useful and realistic results. In the past I have reasonable success using tools like The Grinder (barely maintained and poorly documented, but very useful and scriptable in Python), and even Microsoft's Web Application Stress tool (scriptable in VB). There are probably better tools than these out there but these at least allow you to code a detailed interaction with you site.