Audio
Lame and OGG don't appear to be optimized for four cores, as the benchmark scores did not vary much between the Dell XPS 720 H2C and our own overclocked high-end PC.
Video
DivX appears to get a little extra boost by the Dell system's added cores, but our high-end dual-core system performs very well in XviD by nearly matching it.
Applications
The XPS 720 H2C uses all four of its cores to stomp on both of our custom-built systems in 3D Studio Max. Had we planned to build an "ultimate dream system," we would have chosen an overclocked quad-core processor for the systems we built.