Ask HN: How do you do your user-facing documentation?

This is really two questions in one. We're about to go live with our SaaS offering, but need to put together documentation for our user-facing administrator interface.

1. What forms do you maintain your documentation in? Little "question-mark" bubbles next to input fields? Link to HTML tree on the main page? PDF file?

2. What format/system for managing the documentation has worked best for you? I've done LaTeX and Docbook before, both of which should have little trouble producing nice HTML and PDF versions, but I'm still mulling over the best way to reproduce the info alongside the input fields.

Anyway, any advice is appreciated :)