In the week that I've had the Mac Pro, I've been nothing but pleased with how great this machine is. Along with that, however, is the painful realization that most software has yet to take advantage of all twelve of those logical cores. Aperture is *much* faster than it was on my old machine, but I'd expect to see more parallelization of bulk tasks such as importing.
Importing isn't ideal, but I just noticed that exporting is! Here's a screenshot from iStat of an 80-file export, successfully using my machine's full potential.
I won't hold my breath for better use of the cores in other areas of the app right now, but I will definitely enjoy knowing that exporting will be nearly as fast as it can be.