Disciplined adherance to this approach guarantees that the documentation and code will always remain in synch. However, it often does require that a separate program separate (heh) the code from the comments before compilation.

POD has certain elements of this (but it's definitely not the same). Javadoc is a little closer.

The only person I've seen who really does this is Andrew Johnson, in Elements of Programming with Perl.

In my opinion, it's more valuable on big projects, but it's a good technique when you're stuck on a problem and need to break it down before you can write code.