For those who use emacs with Ruby on Rails, and perhaps even use rhtml-minor-mode, I have published an update:

http://www.welton.it/freesoftware/files/rhtml-minor-mode.el

It now handles .html.erb extensions for layouts/ files and layouts/application.html.erb files (or .rhtml).

Something that would still be nice to see is some hacking to better integrate partials, which currently don’t really know exactly where they fit in their parent document. That would take some work though, as you’d have to scan for use of the partial in question and perhaps do some other parsing of ruby code. If you’re clever though, you could probably get the most common cases by looking for something like :partial => ......