Could you superimpose your graph with a graph of downloaded bitcoin clients / value? The sourceforge has the number of downloads for each version.
downloads can be upgrades of existing users
not all users upgrade to each release
i bet lot of people is happy with hosted e-wallets
While not exact, I think the number of downloads is representative of the total number of users. It isn't an "exact" number, and it has the limit that some versions are more far off from others (in time), but it's still a number, and it's probably better than the number of readers of this forum.
