Looking at the site Web Analytics report, I see that one of our site collections has about 10K "Total Number Daily Unique Visitors" for a given time period. Comparing that number with the count of items on the User Information List shows a pretty big difference - the users list only contains about 4K users.
As I understand it the "Total Number Daily Unique Visitors" is cummulative - in other words if I visit the site each day for 30 days, and I run the report for that time period, 30 of that total number should reflect the visits that I made.
In trying to get a better idea of "distinct visitors for time period" I looked at the User Information List - I can look at the raw ItemCount for total for all time, and do creative things like filter by the Created Date field for a new users during a specific time period.
Are these assumptions I am making correct? Is there some documentation on MSDN or TechNet that covers how the totals in the Web Analytics are calculated and what they really mean?