Want to really know what your visitors do on your site, then this is the tool for you. It actually saves the entire session of the users, the mouse movement, the clicks and the text they enter. Even if they don't click submit or if they get errors in your forms, you'll see all the info just as they saw it on their screen. The form tool is incredible and if you have multiple field forms then this tool will improve your site.
If you use Gmail then this addon is a great one, allows you to track emails you send. See when people open the email and when/if they click a link in your email. Very helpful if you ever find yourself wondering if the person saw that email you sent.