Actually ffdshow multicore builds are taking advantage of those additional cores. I don't know how stable that ffdshow version is.If you need it ONLY for HTPC use I don't see any point in going beyond dual-core anyways, but soon the Athlon II X4 will be is as cheap as the current 45W TDP Athlon X2's, and then everybody will buy quad-core. If you need it for gaming I would shell out the extra cash on the Phenom for sure.
but what does that actually mean in terms of media playback?
Just because it utilises 4 cores does that necessarily mean any improvement in picture quality?