Here are some images which demonstrate what I'm speaking of.
#1 - Lightroom (ACR 3.7) default:
#2 - My custom preset (values in post above):
#3 - K10D ACR profile using ACR Calibrator Script by another user:
I imagine how you see the differences will depend on how your monitor is calibrated. I'm using a fully color-managed workflow and the differences are quite significant, though subtle.
I know it's always possible (and often desirable) to tweak the RAW settings on each import, but my intention here is to find a reasonable "default" calibration to start from that lessens my overall post-processing time.