Yes, basically there are different levels of sponsorship that you can do. It's a way to support the DIS and keep it free for others to use. You can find out about on the FAQ page, I believe. I can't remember for certain. Then in return, each level has some DIS specific goodies that come along with it.
I became a sponsor last year. I figured it was a good thing because this site has helped me out so much in my trip planning and it was a way for me to say thank you to the owners and help keep it going and growing.