On requests, check that you are using browser caching.
Last-Modified should be set.
Expires should be set (seems to be dynamically set if max-age is set on cache-control).
On cache-control - watch out for must-revalidate - this seems to bypass the cache.
This is not good:-
This is OK:-
Cache-Control max-age=1800, public, must-revalidate
NB, public is to allow caching on SSL links.
This is BEST:-
Cache-Control max-age=18000, public
Are the flash files cached?