I love test-driven development. In addition to all the benefits espoused in the books, I found it's extremely useful with my cyclical attention span.
 
I came back to finish a project I'd put down 18 months previous; usually such a long delay means I must spend an hour or two reestablishing context (and afterwards, constantly stumbling across the things I hadn't quite finished but hadn't quite documented for myself to find later; also known as "bugs").
 
But this one I had developed using TDD; I ran the unit test and it listed before my eyes everything I'd worked on, the order I'd done it, and thus reestablished my work flow in about 45 seconds. The very last test was failing, so I knew precisely what I had been working on when I put the project down a year and a half ago.
 
I was making forward progress in under two minutes. World record for me.
 
I love TDD.