For clarification, and this is fact, the only ROMs that are legal for you to own are ones you make YOURSELF from YOUR OWN CART. This is according to the ISDA itself. Directly from the ISDA (http://www.idsa.com/piracy.html):

Isn't it legal to copy video & computer games as a backup as long as you own a legitimate copy?

U.S. Copyright laws permit making a "backup" copy of computer programs for archival purposes. However, the right to make backup copies of computer programs for archival purposes, as embodied in 17 U.S.C. Section 117(2), does not in any way authorize the owner of a copy of a video or computer game to post or download a copy of that game to or from the Internet. Section 117(2) only gives the owner of the copy a right to make an archival copy of the actual copy that he/she legally possesses, not to make a copy of the ROM that someone else legally possesses, nor to post an archival copy of his/her original copy for distribution. Also, there is not an unfettered right to sell "backup" copies. In fact, Section 117 is quite explicit in stating that any archival copy prepared under Section 117(2) can only be transferred to another person if, and only if: A) The original copy is also transferred, and only with the authorization of the copyright owner, and B) The transfer is part of the sale of all rights in the program.

Isn't it OK to copy games that are no longer distributed in the stores or commercially exploited?

No, the current availability of a game in stores is irrelevant to its copyright status. Unlike trademarks, copyrights are not considered abandoned if they are no longer enforced. Copyrights do not enter the public domain just because they are no longer commercially exploited or widely available. Therefore, the copyrights of games are valid even if the games are not found on store shelves, and copying or distributing those games is a copyright infringement. [/u]