Using Alexa, I found some interesting site data.

People ended up on Lernu from searching the following keywords. For example, 62% of people came to lernu after searching for the keyword "Esperanto".
Keywords:
  1.  esperanto 62.08%
  2.  lernu 10.69%
  3.  learn esperanto 5.08%
  4.  اسپرانتو - [Persian - "Esperanto"] 3.40%
  5.  زبان اسپرانتو - [Persian - "Esperanto Language"] 2.76%

The page that users were on prior to visiting lernu. They likely clicked a link to direct them here.
Search location:
1. google.com 23.6%
2. facebook.com 5.8%
3. wikipedia.org 5.4%
4. youtube.com 2.1%

Total websites on the internet that have a link to Lernu:
889

Users on subdomains:
en.lernu.net 30.42%
ru.lernu.net 23.15%
fr.lernu.net 8.37%