Tim Bray: "Over the last twenty years I’ve seen the rise of Structured Programming and Object-Oriented Programming and Message Passing and the Relational Model and those are all good things, but TDD is the single biggest advance in my lifetime. It might (finally) turn software from an amateur’s kitchen to an engineering discipline." While I'm not an expert on TDD, the interactions I've had with teams using TDD (the last project was less than six months ago) has been very positive. Development managers- follow Tim's advice. If for no other reason than to prove to yourself whether or not TDD will benefit your development team (it will). Speaking from my personal experience, it is awesome to see the kind of confidence that a team will develop in their software when following this kind of process. The anxiety normally associated with early milestones and internal demos will be reduced dramatically.
Also, someone needs to tell Tim about NUnit and the TDD support in VS2005. ;)