With help from Martin Albrecht, I've been tracking the traffic to sagemath.org.
Some of the above plots compare Sagemath.org to Maplesoft.com. Before the UW press release (inspired by Sage winning Trophees du Libre), sagemath.org traffic was insignificant when compared to Maple. On Dec 3 when the press release went out until Dec 11, there was a huge spike in traffic, so that sagemath.org went from being a speck to over twice the amount of traffic as Maple gets. NOTE -- this increase in traffic started two days before the slashdotting. On Dec 5 during the slashdotting, the number of downloads of sage itself went up a huge amount (thousands per day). This hump died down after about a week on December 11. However, the number of Sage users has gone up by quite a bit, and perhaps a nontrivial fraction of the people who tried Sage a week ago are now Sage users. Traffic to sagemath.org has gone from basically nothing as measured by Alexa to nontrivial in comparison to the other big Ma*'s.
Perhaps soon trac #1000 can be closed and replaced by a ticket to have 100,000 users?