In some countries, circumventing copy protection is illegal, so depending on where you live, ripping GC discs (which are encrypted AFAIK) may be illegal. At least one court case in the US has ruled that circumvention of the protection on DVDs, such as in the case of media PCs that store movies, is acceptable though. Add that to the fact that you're using Nintendo's own hardware (trying not to get too specific here) to rip the content and I doubt any legal action against someone who ripped their own GC game for their own personal use would stand up. But that's just for copy protected games like GC games.
Other games, such as PSX games have no copy protection, so anti-circumvention laws do not apply to them. Still, since ripping is commonly associated with copyright infringement, it's probably prudent to avoid its discussion on forums such as these, especially since it's easy to Google and find the answer to your questions.