On SearchSoftwareQuality, there is a section called Ask the Software Expert where a "guru" answers someone's question. Scott Barber has a post for Understanding performance, load, and stress testing that I find amusing.

The content is nothing that most web developers would find particularly noteworthy, except this pithy conclusion about the underlying myth of performance testing:

Experience tells me that these questions stem from the myth that "performance testing is just functional testing, only with more users." This simply is not the case. One will not meet with success while performance testing, except by accident -- which does happen quite often -- by treating it like functional testing. Not only are the skills, purpose, planning, scheduling and tools different, but the entire thought process is different. To tell the truth, you are probably more likely to succeed by simply asking the members of the team "what would you like to know about performance?" and then figuring out how to collect that data than by treating performance testing like a functional testing project on steroids.

Now I may not be as smart as Scott Barber, but I do know a cool storm picture when I see one. Storm your site with virtual users to find out its performance under load. Metaphorically speaking, it should be like this picture: