I was relieved to browse the Aperture library and see that the vast majority of images that I’ve captured fit into the SIgma DP1 parameters: ISO 800 or less and F/4 or smaller apertures. With the D300 and its Auto ISO, I’ve captures quite a few outside of it- ISO 1600 at f/2.8. So while I’d rather have the D300 sensor and 24mm 2.8 in a compact package, I’ll give up 2 stops and continue to consider the DP1 sensor with an f/4 lens.
On the other hand, I suspect that the DP1 doesn’t beat a Leica plus Summicron. My f/2.0 lenses give me 2 stops over the f/4 of a Sigma DP1 and my ISO film is just a stop slower than the ISO 800 of the DP1.