Front Row - CPU or GPU?

I'm not an expert, but GPU, at least on newer Macs. Assuming it's the same as most similar Apple technologies, if the GPU isn't sufficient to handle it (that is, doesn't offer sufficient programmability) THEN it gets dumped off to the CPU. That's why the fancy transitions on Keynote (for example) aren't available on a machine with older graphics cards--they can't be handled in real-time by the GPU, so they're not even available. Other apps hand it off to the CPU, if the real-time-ness isn't as critical.

That's probably what's going on with CoverFlow in your example. I note that it and Front Row barely even touch the CPU on my MBP, probably not because it's so fast but because the GPU can handle it.

On a wildly unrelated note just because I feel the need to say it "out loud", speaking of CoverFlow, I just found out that it supports a full alpha channel for transparency in PNGs--you can do some awesome stuff with that.