We all know that while we have over a million, actually over 1.2 million now, user accounts, the number of actual contributors is quite a bit lower. Often you will see a number of 200'000 quoted, however that only considers the last editor of an object and not all the editors.
Analysing the mid May 2013 changeset dump gives a total of 335'000 unique user ids that have created a changeset. We can see this number increasing more or less linearly in recent years:
Over the last 12 months we have averaged roughly 7'000 new contributors per month, in total a good 80'000 per year:
The numbers only take half of May in to account so it is too early to see if the announcement of the iD editor will already have a noticeable effect. In the long run we hope for a clear increase in the number of account holders actually contributing.
May 2013 numbers now for the whole month, based on the early June changeset dump. Total number of contributors 340'311, new in May: 9357 While this isn't a new record it is a good 2nd place.