I started looking around for demo apps that had the components I need and handily bonked into webkit.org/demos/sticky-notes/ I dream of a competitive WebOS device so it is nice that iPhone and WebOS should have very similar implementations. Here's the first bit of goodness.
$ curl --include http://webkit.org/demos/sticky-notes/StickyNotes.manifest
HTTP/1.1 200 OK
Date: Thu, 11 Mar 2010 06:01:37 GMT
Server: Apache/2.2.14 (Unix) mod_ssl/2.2.14 OpenSSL/0.9.8l DAV/2 mod_python/3.3.1 Python/2.5.4
Last-Modified: Sat, 13 Jun 2009 00:53:08 GMT
There are some important rules going on - this bit is telling the browser exactly what resources to make available when the application is in offline mode. Sticky Notes is mostly CSS so the manifest is micro but it's still a good start. Some bits that I've picked up in other places: the page that includes the manifest= is automatically whitelisted; fallback is how you replace resources with an offline-specific image or resource; the content of the manifest has to change for the browser to recognize a difference - it isn't the timestamp or the filename / path.