I've been a user of StackOverflow for 18 months now; it's an interesting and useful site, and I enjoy participating.
I don't put a lot of time into the site, but I do visit almost every day, and generally interact in one way or another.
But after 18 months, my reputation is only slightly more than 500.
And yet, though StackOverflow as a institution is only a few years old, there are users with hundreds of thousands of reputation!
According to the privileges list, I have about 60% of the privileges, so I guess I'm making progress.
I'm not sure why it matters; I'm just sort of noticing it.
But, anytime there's a measurement, and I'm one of the people being measured, I'm always intrigued...