MAC compression produces .ape files, I think it's two names for the same thing. Definitely not worth converting / downloading them, but if you're ripping your own CDs for example I think it could come in handy. It does produce pretty large files though, from my brief experiments with it. I don't think my ears are sensitive enough to tell the difference between an MP3 and a real CD anyways. Ah well.

<i>A CD rip will never reach the same quality as the original no matter what compression you intend to use. </i> --Bulldog

Why can't it be lossless? It's not that hard to do lossless compression on something, and anything that's losslessly compressed can be decompressed back to the original. I'm assuming it's decompressed on the fly as you listen to it, so to the computer it's a 100% perfect copy of what it could read off the CD.