It is certainly true that copyright laws do vary across international borders, although there are a number of international agreements in place. That being said, to my knowledge, no US court has ruled that format-shifting is a legitimate reason for making personal copies. Time shifting has been determined to be fair use, but not format-shifting. To my knowledge, US copyright law does not permit the ripping of CD's.
One thing that we keep in mind about copyright law. The copyright belongs to the owner, and it is up to the owner to decide what is and is not legitimate copying. If Shania Twain (or her producer whoever actually owns the copyright), were to annouce that anyone can copy, rip, share, download, convert to MP3 any song from her latest Up! CD, then it's perfectly legal for everyone to do so. The owner of the copyright sets the boundaries, not copyright law. The law protects the copyright owners ability to set the rules. The confusing aspect is that copyright law has enumerated a short list of the types of copies that are considered "fair use", and therefore outside of the control of the copyright owner. Many, many people, just like in the scenarios presented by pmonett above want to decide for themselves what is and is not fair use and permitted. But that is just plain wrong. If what you want to do is not covered in the enumerated "fair use" provisions, then you're bound to the wishes and restrictions of the copyright owner. Whereas exact duplicates for backup purposes has been deemed fair use, format-shifting has not (at least within US copyright law) and until such time as it goes on that list, it's safe to assume that any type of format shifting is a copyright violation.
Good Luck
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As a circle of light increases so does the circumference of darkness around it. - Albert Einstein