i seriously doubt rack manufactures care about taking the best care of cds. they are selling an item to make a profit, not to care for your collection.

gravity is an enemy when storing cds flat. eventually, gravity can peel the layers that make up a cd apart. that said, it is not a problem that rears its ugly head often. libraries, archives and government agencies store information on optical media in an upright position. there is a reason for it. but hell, they are your discs, so store them however you like. myself, i store them like a book, in cd cases in a controlled environment.

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EDIT:
someone will likely call out my gravity idea, so hopefully this will clear things up. it all has to do with mass - a disc is more affected by gravity when flat since more of its mass is exposed to it.

"Here on earth, gravity pulls stuff down. In fact, that's what we mean by "down" -- it's the direction in which stuff falls when you drop it. The ordinary ("Newtonian") view of gravity is that it is a force which attracts objects to each other. Forces can bend objects. If you hold a long, bendable object on one end, gravity pulls down on the whole thing, and the object will bend downwards. A diving board will bend under its own weight. Gelatin dessert bends under its weight. People who design buildings and bridges and such stuff have to worry about the weight of all the material pushing down on supports, bending things. I once heard on the radio show "Car Talk" that even the hoods of some cars can sag downwards if they are not properly braced. Wires between telephone poles and electricity distribution towers sag under their own weight.

... "

A diving board bends at one end because the greatest amount torque is produced by the mass of the board most distal to the joint. A CD is perfectly symmetrical, and weighing some trivial amount and nestled tight and proper in a CD case, there is no way any appreciable amount of "warp" is going to occur (putting aside the dubiousness of your first claim regarding peeling occurring in any case).

First off the cases would all have to bend and warp before it would get to the disk.

I don't think that the Earth's gravitational pull alone is enough to warp a floating CD significantly. Maybe if you waited a million years...

A combination of heat and pressure against a non-flat surface will do it in much shorter time.

That would be a very sad "sight," (not to mention it's kinda sad that people care about shit like that...good thing I didn't show my REM or U2 discs...) and I dig your sig btw. Very true!

Come to think of it, I'm actually a little disappointed no one griped about my Ill Nino cd in there...

i seriously doubt rack manufactures care about taking the best care of cds. they are selling an item to make a profit, not to care for your collection.

gravity is an enemy when storing cds flat. eventually, gravity can peel the layers that make up a cd apart. that said, it is not a problem that rears its ugly head often. libraries, archives and government agencies store information on optical media in an upright position. there is a reason for it. but hell, they are your discs, so store them however you like. myself, i store them like a book, in cd cases in a controlled environment. "

There's also that CD-eating fungus to worry about if you live in warm, humid climates (like me). It's also mutated to eat vinyl too.

I'm not making this up, btw:

http://www.stereophile.com/news/11073/

Wow but how much time are we talking about here for that to happen? Because surely that would affect anything stored flat...

I know some people burn their cds right after they purchase it, and then store the original in a safe place. They just listen to the burned version, and one day if anything happens, he can burn the original again.
It's pretty intelligent but I don't have the time or the courage to do this. I have too many cds to start doing this now...