bit off topic, but....
I've set up my first Centos gateway server and now setting up another server on internal network.
I thought it would be nice to use the gateway servers "/var/cache/yum" as a local repository for any internal servers since it would be up to date with the lastest packages and save bandwidth.
It will only contain those updates for packages that are installed on the system. And usually a gateway system only has a minimum set of packages.
That's all I wanted.
If you look for an integrated solution, you could look at Yam:
I'll take a look, but I thought what I wanted to do would be do-able.