Thanks CANDY,

I visited their site just now and it says this,

"How do the Summary Stats work?

The 'Summary Stats' determines whether a visitor has been to your website before by using a cookie. So if a user has cookies disabled we have no way of knowing if they are unique or not, and will by default be considered unique."

I guess it's not very reliable because most people now disable cookies.

Also, the IP thing doesn't work very well either as a lot of people have 'dynamic web proxy' IP's, they get a different number each time they visit a site.

I guess the answer is that there really is no one sure way to keep track.

Thanks again

Correct. All hit counters have the same problem.

You could try Google analytics - it's simple to use (just pasting code to each page you want to keep track of)
http://www.google.com/analytics/