Unbearably Slow Copying From NAS and/or External Drives

I've read many posts (Some here, some on other sites) but have found no explanation nor solution to this problem: if you have thousands of file on an external drive or NAS and try to back this repository up to another unit, the Finder not only takes a CRAZY amount of time "preparing to copy" but if and when it gets past that stage, isn't particularly efficient and/or fast.

Is there a technical reason about OS X, the Finder or copying over ethernet that is documented somewhere? I do know that this is not as bad on Windows and while this may not be the biggest problem for many people, with more audio, video and other data being collected...it seems like it will be.