Files such as css and js should be far future cached, there should be a header like: Cache-Control="max-age:525600". As originally implemented in http://jira.magnolia-cms.com/browse/MAGNOLIA-3297

But the files with .cache. in the url do not have any Cache-Control header set. For example look at this file on demopublic:
http://localhost:8080/magnolia-bundled-webapp/resources/templating-kit/themes/pop/css/mobile.2013-01-25-11-12-21-633.cache.css

Debugging on my local instance it looks like the executor which gets run for this file is Bypass. Bypass contains two executors.
#1. setExpirationHeader - which looks like it is working great - adding a really long Cache-Control max-age.
#2. executor.Bypass - which just continues down the filter chain.

Could it be that the executor.Bypass somehow nullifies the effect of the setExpirationHeader?

Im not an expert on the Cache module - perhaps there are timing concerns or something else. But it appears to be a problem.