Testing usability of digital history sites

I’d like to propose a session that covers some of the options, guidelines, and pitfalls of using focus groups to provide feedback on digital history sites at various stages of the development process, from early planning to beta testing. How can we do this in a useful way that doesn’t derail the project schedule? How do we maintain the proper tension between our goals for the site and simplicity/usability so that we make room for audience feedback and participation without devolving into watered down “groupthink?”