I've just made some tweaks to allow client-side caching of article pages and recentchanges.
They now provide a 'Last-modified' header which reflects the timestamp of the page (or for recentchanges, the most recently modified page). They're still set to expire instantly, so a caching client ought to ask for the page again, with an 'If-modified-since' header. If the last-modified timestamp has not changed, we tell it '304 Not modified' and the client uses its cached version. Otherwise, the page continues being generated and loaded.
Currently on test.wikipedia.org, please throw various browsers against it.
-- brion vibber (brion @ pobox.com)