I know, I was just trying to figure out how this was supposed to work. Currently setting Last-Modified seems to be the only way to get something cached in Apache; Expires alone is no good, and adding an Etag header doesn't seem to have any effect either. Maybe this should be classified as an Apache problem? Shouldn't Apache cache pages that have Expires?
Please keep in mind that **Apache is not a cache server**, it has caching attached more like an afterthought to the mod_proxy. If you want predictable caching you will need to use real caching software such as Squid. I personally have moved away from Apache even for small websites since there are some other issues with Apache caching, such as zero-length responses in some cases. jens