As long as Squid isn't overwriting those headers, as we do for Cache-Control. :)
Squid is overriding at the edge all text content CC headers into:
Cache-Control: private, s-maxage=0, max-age=0, must-revalidate
MediaWiki Cache-Control is used internally though. This allows us full control on lifetime of object with application only, no need to tweak any squid stuff.
Yeah, special cases suck. :(
Especially when they're just eye-candy for english-language site.
Domas