Whenever someone gets on the site for the first time during the day, it increases the uniques count once per day for that user - but there is a different count for how many times it gets clicked on -
Now my own "unques" count on my own web software reads a little differently:
The bandwidth dropped a lot after compressing the pages before they were sent out.
The funny thing is last year when I did this we ranked about 21-22 on average - now we've been bouncing between 16 & 18 but the site is more than twice as busy as last year and I noticed that alot of the same sites from last year are in the same rough mix this year...