Hey all, I applied for the GRFP in 2010 and 2011 and received an Honorable Mention in 2011. My area of research is social learning and cultural evolution, so somewhere between Biology and Anthropology, but I believe I submitted as Animal Behavior. I wrote up a blog post recently where I provide the full content of my three essays from 2011 and give some advice from my experiences:
http://www.cultevol.org/2012/10/writing-for-the-nsf-grfp/
Hopefully someone will find it helpful. Let me know if you have any questions about what I wrote (comments on the blog or a personal email would be best, as I won't check back here often). Good luck to everyone applying this year!