Jamie (fearoffish) and I are working on improving the docs for Rails.
We're making "top-level" progress right now, documenting/re-documenting high level things that need to be improved, but on our lower passes, we'll drill down to this level and document every options hash, every argument, and so on. It'll take us a little time to get there, but we're working on it.
If you want to watch our progress (we work all day, every Monday), then you can check out http://fearoffish.clientsection.com/ and use login guest and password guest.
Thanks! Jeremy