I, for one, see it every day at work.
(not that I’m a statistically relevant sample, but still)

The W3C claims 38% of browser users are on XP. I think that we can safely assume that at least 90% of people who still use XP have no idea how to change rendering settings. Internet World Statistics estimates that there are 2,095,006,005 web users worldwide. So my guess is that at least 716,492,052 web users around the world are still on XP with default settings.

Related: This post and the comments below.

I think the methods for getting these numbers haven’t changed since you last brought this up, though the percentages probably have.

My accurate numbers for last week:

Out of a total of 6159 browser requests to a general interest site, 1439 came from Windows XP (including bots claiming that they’re on XP). Of these 1439 requests, 663 came from browsers that can display web fonts, but don't override the ClearType settings of the system. That’s 10.76 % of the total requests.

In other numbers, of 129 requests to the web fonts files, 19 (14.7 %) came from browsers on Windows XP that respect the system font rendering settings.

I know you asked for »how many users«, not for requests, but counting users is hard, and counting requests gives a more accurate reperesentation of real usage (think of one user using ClearType, but only reading one page vs. one user without ClearType reading 20 pages).

Thanks Jens. These numbers are good. I can’t help think many would upgrade beyond IE6 even though they are using other browsers. Perhaps the numbers are even better.

Anyway: The last time around, the answer was close to 30 % (based on similar numbers from Wikipedia). Statistics grow more accurate with quanitity, so keep em coming.