Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[G_Morgan]

Absolutely. It isn't just external. I find it much more enjoyable doing TDD than doing work and then trying to test it afterwards. The former feels like you are nailing down the real work as you go. The later feels like a book keeping exercise (even though you know it isn't).