A recent whitepaper called Managing a Successful Performance Lab was just brought to my attention, if you're about to perform a performance or stress test this whitepaper is for you. Even though it is written in the context of BizTalk Server 2006 I think you can utilize the techniques described in many types of applications, use it as a template and utilize the parts that apply to your application.
Please note that this whitepaper is not only a high-level discussion, it provides sample on purposes, testbeds, gathering of results, checklists, etc. The abstract says:
An essential part of every mission-critical application’s pre-release testing should always be simulated performance and stress testing. This paper outlines some key strategies for managing a successful performance lab with Microsoft BizTalk® Server 2006.