Well SharePoint MVP Andrew Woodward thinks so. Check out his paper on doing test driven development with SharePoint. His paper walks you through building a Web Part the TDD way. I haven't had a chance to read It but I'm really interested in this.
Beginners Guide to Test Driven Web Part Development
About KyleKelin
Kyle Kelin has been implementing software in the Microsoft space for the past 6 years mainly as a consultant. His interests are SharePoint, .NET, JQuery, and Silverlight.