mysticwolf said:
Emulators are legal. However, basically the main thing one does with emulators is use ROMs. ROMs are illegal
Right from the Nintendo Corporate Info site:

http://www.nintendo.com/corp/legal.jsp#emulator

Can I Download a Nintendo ROM from the Internet if I Already Own the Authentic Game?

There is a good deal of misinformation on the Internet regarding the backup/archival copy exception. It is not a "second copy" rule and is often mistakenly cited for the proposition that if you have one lawful copy of a copyrighted work, you are entitled to have a second copy of the copyrighted work even if that second copy is an infringing copy. The backup/archival copy exception is a very narrow limitation relating to a copy being made by the rightful owner of an authentic game to ensure he or she has one in the event of damage or destruction of the authentic. Therefore, whether you have an authentic game or not, or whether you have possession of a Nintendo ROM for a limited amount of time, i.e. 24 hours, it is illegal to download and play a Nintendo ROM from the Internet.

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Are Game Copying Devices Illegal?

Yes. Game copiers enable users to illegally copy video game software onto floppy disks, writeable compact disks or the hard drive of a personal computer. They enable the user to make, play and distribute illegal copies of video game software which violates Nintendo's copyrights and trademarks. These devices also allow for the uploading and downloading of ROMs to and from the Internet. Based upon the functions of these devices, they are illegal.