I find the GH2's ISO160 minimum to be one of the most annoying little things about the camera. I understand that it resulted from Panasonic's decision to correct the inaccurate ISO calibration of the GH1, whose ISO settings are about 1/2-stop underrated across its range (e.g. GH1 ISO100 = GH2 ISO140). However, the absence of ISO100 on the GH2 makes it awkward to match minimum-ISO exposure with other cameras. Often I'll resort to using ISO200 across the board, if only to simplify things.

Something is definitely suspicious about the noise jump from ISO250 to ISO320 in the video above. I notice a similar increase in noise from ISO1000 to ISO1250. Consumer cameras often use digital scaling to simulate the 1/3-stop increments between the standard full-stop settings. From this video it appears that some of the 2/3-stop settings may be digitally downscaled from the next higher full-stop setting, e.g ISO320 = downscaled ISO400 exposure.