I've moved onto part 2 of Pickaxe. Currently on the RDoc chapter. I must say I'm impressed how smiple it seems to keep things. No fancy @param annotations to learn, just put a comment above your class / attribute / method and you're off. If you feel the need for more control of your formatting, you can get busy with a very wiki-like syntax.
Its also interesting to note that if you click on a method, RDoc will show you the code. It highlights a key difference between the Java and Ruby worlds.