Thought it'd be intersting to post this link I seen, its all about the laws of video game 'backups'.
http://www.emulationzone.org/articles/general/how-to.htm
So a few quick points from it.
U.S. law allows you, the owner of a software product, to have three (3) copies of that product at once: the original, an installed copy, and an archive copy. The law does not give a definition to these terms. So, in the sense of a ROM image, you can arguably say that the image on your harddisk is being used to play Zelda 1 is the "installed" copy, the cart that you bough 10 years ago is the "original" copy and a copy of the ROM image on a floppy disk, tape, website or other medium is a "back-up" copy. But, only one of them can be in use at once. So, playing the game on your NES and on the PC at the same time is ILLEGAL.
"But Nintendo has this on all there game manuals:"
WARNING:Copying of any Nintendo game is illegal and is strictly prohibited by domestic and international copyright laws. "Back-up" or "archival" copies are not authorized and are not necessary to protect your software. Violators will be prosecuted.
Nintendo is trying to intimidate you. The law is the law, and you are allowed to have up to three copies of your software. If they don't like it, tough! If you didn't agree to their terms when you bough the software, then don't worry. If they don't like it, tough!
The "Gift Policy"
I didn't believe this when I read it. It took me several scans through one part of the bill to fully understand a section of the 1997 anti-pircay law that I will refer to as the "Gift Policy." I believe congress passed this part of the act because it is not right to arrest and/or fine someone who was sharing a program that they bought in the goodness of their heart to a friend. But a line had to be drawn, so there is a limit of how many friends you can have.
As owner of a software product, you are allowed to make up to 10 copies of your software and give it to someone as a "gift" to someone. You can distribute that many as long as the total purchase cost (the cost of the software when you bought it in the store,) of the duplicated software does not go over $1000. So, if you bought Zelda 64 for $85 and you have a ROM copying device, you can legally give that game to 10 friends. LEGALLY. (85 * 10 = 850 < 1,000)
The "24 Hour" Rule
As far as I know, this law does not exist in the US law books. In fact, I think it was removed during the 1997 Anti-Piracy bill, but I could be wrong.
I hope this settles the questions about basic 'backups'.