i try to keep them seperate and as neat as possible but its not easy. as long as your not a mess is it really bad for audio and video if the wires in the back of your rack system are not ideally neat. does it really effect quality because its so hard to do when you have a lot of components and space is limited.

Perfect neatness is pretty close to unobtainable, and to be honest I can't really even claim much semblance of order at all behind my cabinet. As long as you aren't getting noise (hum/hiss or the like) from power cords upsetting other cables, you're probably just fine.

I've got to admit I'm a bit of a neat freak when it comes to cable management. I've gone so far as making my own analog video and audio cables so they can be the necessary length. However, I think it is most important to make sure signal cables are separated from power cords. If they do cross make sure they are at right angles to each other. I also don't like loops in any cables if possible so using cables that are as close to the correct length is important. Finally, use good quality cables (including their connectors) and most, if not all, interference issues caused by a mess of cables that look like spaghetti can be avoided.