Cristian Sorega has an enlightening series of comparisons between the Ricoh GRD I, GRD II, GX100, and Panasonic LC1 over at Ricoh GR-Diary. Check it out if you're interested in any of these cameras but especially if you're wondering how the GRD I and GRD II compare.

Links:
GRD I vs GRD II - Teaser no. 1
Black and White Comparison
RE
Color Comparison - Part 1
Color Comparison - Part 2