Now, I'm certain some people would disagree with me, but if I were to classify the Cell processor I would call it a HD-DSP more than either a conventional CPU; and I certainly would not call it a CPU-GPU hybrid. In fact, if I remember correctly, one of the main purposes of Sony (and Toshiba) working with IBM to develop the Cell processor was that they needed a next generation DSP.
DSPs are cool because they can outperform a conventional CPU at a tiny fraction of the cost on tasks that the DSP is well suited for; unfortunately, it only makes sense to use DSPs on "Simple" tasks (ie, programs that only require a few thousand lines of code) that are run on systems that are mass produced (like MP3 players) because they require dramatically more effort to get anything to run well on them, and you can easily lose money from development costs if you produce software that is too complicated or your hardware run is too small.
