There are some sites out there that do use it, and I think its pretty interesting to see which people from what country are viewing the board. Or have viewed it x time.
But aren't all flag counters the same ? I think so but in any product there must be competition.
This one looks alright to use on your site:
Description: With your free account from 99counters you can now create customized web counters for your website, blog and social network profiles.
Using 99counters is a powerful and effective way to get instant web statistics.
But I think this also is a pretty good one!
Description: Add a free Flag Counter to any webpage and collect flags from all over the world. Every time someone from a new country visits you, a flag will be added to your counter. Not only will this make your site far more interesting, but clicking on your Flag Counter will reveal amazing information and charts!
Enjoy this resource.