A quick and easy way to capture basic referral information (the URL that referred the visitor) is to use a bit of javascript and look for the 'document.referrer' value. There's no 100% guarantee with this, but it's a good way to capture most referrers and see where they're coming from and what they may have searched for to get there. Here's how to set this up:

1. Add a new "hidden form field" in your form called "referrer" (the name doesn't really matter as long as it matches the next part)
2. Add the following script into your "Javascripts" section in the bottom left of the editor and set the Placement to "Head":
   
   

   <script type="text/javascript">

   jQuery(function(){

     jQuery('input#referrer').val(decodeURI(document.referrer));

   }); 

   </script>

That's it! You should start to see "referrer" showing up in your leads data and your email notifications.

How do I interpret the referrer data?

If I search google for "landing pages" and hit the Unbounce.com link that shows up, my referrer information looks like this (I've broken it up into multiple lines):

http://www.google.ca/url?sa=t&source=web&cd=2&
ved=0CEEQFjAB&url=http%3A%2F%2Funbounce.com
%2F&rct=j&q=landing%20pages&ei=VEKjTdLrN8ffiALDuKyGAw
&usg=AFQjCNEdp5atllJolLmui3JnJ-LeqkqI7g
&sig2=WWeqREq70WX5qNiwMh3oIw

You'll notice the data is a bit unreadable at first (it's encoded, the script you're copying above will help decode it) but you can still see that the domain is google.ca and that the search query (represented by 'q' in this case) was landing pages (the %20 is just a space). Hope this helps you learn more about your leads!