17.7 million unique IP addresses
As I'm sure I won't be the only one to mention, this is an overestimate, and surely a large one, of the number of installations. After all, most people at home have DHCP from their ISP.
More useful, even if still not perfect, would be to know the daily number of unique IP addresses downloading updates -- since it's much less likely that the same installation will perform updates in one day using different IP addresses. That could be presented as either an average (not so good, since a few days after updates are out most will have applied them, numbers fluctuate and skew the average) or as a graph of the raw numbers. Or some combination, like the average for the peak day in a month. Something else, because 17.7 million since 2007 means nothing. Could be 100,000, or 1 million, or more, or less. How many times in a year does the average home computer change IP address?
That might give a better idea of the number of Fedora installations out there.