We think of testing in 4 phases: (1) developer testing, (2) in house testing, (3) beta testing, and (4) customer testing. In the (distant) past, we pretty much relied on 1 and 4 exclusively. Over the years we have ramped up our in house testing efforts as our staffing allowed and have recently been shifting our emphasis on customer testing to a true beta program. This latter effort is really a formalization of our old customer testing paradigm. The formalization of the beta program allows customers who are interested in testing and being on the bleeding edge to do so. Other customers who aren't as comfortable with that type of situation aren't put in it. This 4 phase model is appropriate for a vertical market solution, and not so much for a custom project. For custom projects, we rely more heavily on developer testing and customer testing. We find that as long as you're up front with the customer about testing expectations, customer testing can be a really powerful tool.