Back in 2007, I contributed my first major piece of Drupal documentation. It was a tidying-up exercise, really: improving and clarifying KarenS and others' existing documentation for the Form API workflow. I had completely forgotten about it, until kae76 on #drupal-uk IRC mentioned that she'd found it useful in a D6 context, and wished there was an equivalent for D7.
Now, inspired by that comment, I've started all over again; I'm preparing notes for a D7 version. The notes as they stand should be sufficient to muddle through if you need to; even to build a similar workflow, if anyone fancies doing so themselves. But with any luck the next step will be for me myself to turn them into a suitable diagram: watch this (RSS) space if you're interested; or chat to me on Twitter if you'd like to help out.