Just got directed (via Richard Seroter) to Rob Steel's blog on BizTalk performance. He is putting together what he refers to as the BizTalk Performance Lab Delivery Guide, which is the process his team has established for successful BizTalk testing. Go check it out at BizTalk Performance Explorer!
If you've ever been tasked to test BizTalk you can get a jumpstart from reviewing this blog. If your managing a BizTalk testing engagement, or any testing engagement for that matter, you'll still find good information around lab process(es). He's also posted links to several other relevant BizTalk testing information.