Since the Kindle and Cybook Gen3 and Sony readers are all "relatively new," my general rule of thumb for equipment sold (ratios) is the comparing the number of people browsing each of the forums over a period of time (say every hour for a day or two, or same clock-time over a few days). Within a small percent error, this *should* give us the ratio of the number of units sold on each.

Perhaps it is too 'statistical' for some people.