I just finished re-reading Martin Fowler's Mocks Aren't Stubs from 2007. I wasn't as experienced then in the various forms of agile development as I am now, so couldn't quite appreciate his perspective until somebody (and I'm sorry I can't find whom) brought up the paper again in a tweet a month or two ago. (Yes, that's how far behind I am; how do you do when you're working 15- to 18-hour days, 6 or 7 days a week for 6 months?)
In particular, the distinctions he draws between "classical" and "mockist" test-driven development (TDD), and then between mockist TDD and behaviour-driven development (BDD) are particularly useful given the successes and challenges of the last dozen or so projects I've been involved with. I wouldn't quite say that many teams are doing it wrong. They/we have been, however, operating on intuition, local folklore and nebulously-understood principles gained through trial-and-error experience. Having a systematic, non-evangelistic, nuts-and-bolts differentiation and exploration of various techniques and processes is (and should be) a basic building block in any practitioner's understanding of his craft.
Put (perhaps too simply), the major distinction between classic and mockist TDD is that one focuses on state while the other focuses on specific, per-entity function; projects that mix the two too freely often come to grief. I believe that projects, especially midsize, greenfield development projects by small or inexperienced teams should pick one approach (classic or mockist TDD, or BDD) and stick with it throughout a single major-release cycle. You may credibly say "we made the wrong choice for this product" after getting an initial, complete version out the door, and you should be able to switch the next full release cycle to a different approach. But if you don't know why you're doing what you're doing, and what the coarse- and fine-grained alternatives are to your current approach, you can't benefit from having made a conscious, rational decision and your project thus can't benefit from that choice.
Anything that gives your team better understanding of what you're doing, why and how will enhance the likelihood of successfully delivering your project and delighting, or at least satisfying, your customers. Even on a hobby project where your customer is…you yourself. Because, after all, your time is worth something to you, isn't it?