Does "build up" on the bottom of copper-bottom stainless sauce and frying pans matter? I am not the most fastidious pot washer: over the years, my copper-bottomed fry pans have developed a layer of (I guess) burned oil residue.

Aside from any "ick" factor, does this affect the the performance of the pan? I've been trying to scrub a little bit off every time I wash them but when I have seen cooking shows, etc. I see pans that look like mine.

Does it matter? And if it does, is there a way to get this off aside from brute force with a ScotchBrite pad?
I think it depends on your cooking surface.

If you're using gaz, induction or coil, then it should be ok.

If you are using a glass top, then the contact between the pan and the glass will not be efficient, and you will loose some of the heat.

I would spend some time cleaning it up.