To Clarify, the Cell's SPUs can act as very powerful and flexible stream processors. This due to very high internal bandwidth and very high speed dedicated memory available to each SPU.
For example when anti-aliasing is done on the SPU or when processing 7.1 surround audio, small chuncks of data is processed at very high speed, just a small part at a time. Regarding graphics and audio processing the Cell is most excellent for stream processing.
Executable code is usually of course much smaller, each SPE can act as independently operating systems on a chip as well. The Cell is very flexible and powerful with regard to what they can do with SPU optimised functions. It's more powerful than top PC processors and far more flexible than GPUs.