I have two systems at home running Archlinux, and even with an almost identical configuration. Isn't it a waste to update these systems independently, and thus to download the same packages twice? But of course it is!
I've searched for 'local repositories', but did not find the possibilities discussed in the pacman wiki entirely convincing. Days later, I stumbled across a discussion on the archlinux forum on pacserve,, which proved to be exactly the solution I wanted. The speed of updates across the wifi is something I can't get enough of. ;)