It's funny, because I feel like TDD -- not just unit-testing, but TDD -- is most helpful when things aren't well-defined. I think back to "what's the simplest test that could fail?" and it helps me focus on getting some small piece done. From there, it snowballs and the code emerges. Obviously it's not always perfect, and something learned along the way spurs refactoring/redesign. That always strikes me as a natural process.

In many ways I guess I lean maximalist in my practices, and find it helpful, but I'd readily concede that the maximalist advocates are annoying and off-putting. I once had the opportunity to program with Ward Cunningham for a weekend, and it was a completely easygoing and pragmatic experience.