On a more technical and less psychoacoustic angle, an mp3 can never be 100% CD quality. It will never have exactly the same data as the CD, because mp3 is a lossy compression format. I suppose if you had a 705.6 kbps mp3, (which is not supported by the specification), it could be lossless, but you might as well just use a WAV at that point, as the size would be the same.

But, as Bruno said, depending on your ear, mp3s can sound as good as the original CD without getting even very close to that.