I love to know who's visiting my site, where from, and what they are looking at. Its interesting information in and of itself but it also helps greatly when adding advertisements to your site. Another thing I like to look at is how many people are using FireFox versus that other internet browser

Google has a great free service called Google Analytics. All you have to do is sign up for the service and then you can have a fairly high quality visitor tracking service. Here's how you get your Drupal site set up with Google Analytics.