hyena64: "US unique visitor". All that means is someone logged on that "supposedly" is new to the site, then came back at least once using the same IP address.
They don't have to come back, one visit is enough.
I found this article in Wikipedia about Unique Visitors interesting. The first couple of paragraphs is enough. Highlights:
-It uses IP addresses + a further identifier (usually a cookie)
-It identifies computers, not unique people visiting a site. So if more than one person uses that computer and visits the site, you still get just 1 unique visit counted.
-"Unique users is a common way of measuring the popularity of a website and is often quoted to potential advertisers or investors."
-If you clear your cookies, you get counted again. Hmmm...
Monthly updates, we clear our cache(which in my case also clears cookies) do I get counted twice each month? Is the real number of unique visitors in November 2012 not 413K but closer to 206K?
Anyway, I'm more interested in the trend than the absolute number.