A very rough estimate of the number of unique visitors can be obtained
by hits to the stylesheet:
Screen Stylesheet:
http://www.softwareproblem.org/good.css
Print Stylesheet:
http://www.softwareproblem.org/evil.css
Here is my command line:
# grep "GET /good.css" access_log* | wc
1757 28950 311391
What that means is that the screen stylesheet has been hit 1757. That
is an upper limit for the unique visitors, because of course some
visitors empty their browser caches then visit at a later date,
thereby loading the stylesheet a second time.
I'll set up proper log file analysis with Analog next week sometime:
http://analog.cx/
-- Jon