Today, September 22nd, is the birthday of both Bilbo and Frodo Baggins, two of the most well-known and adventuresome Hobbits to ever venture forth from the Shire. You may be familiar with their adventures from J.R.R. Tolkien's books, The Hobbit and The Lord of the Rings, or from their film adaptions.
To celebrate Hobbit Day, you could curl up with Tolkien's work, and probably a delicious snack or two (or three!). It's tradition in the Shire, to give gifts on your birthday, so you might consider surprising someone you know with a small gift or card. The truly ambitious might consider building their own Hobbit Hole, for guidance, take a look at this Welsh family's home.
You can read more about the origins of this holiday on Wikipedia.
You might also enjoy catching up with the developments of Peter Jackson's upcoming (2012) film adaption of The Hobbit. Check out the official blog (with video) here: www.thehobbitblog.com
For more online fun, try out the Hobbit Name Generator. In the Shire, I'm known as Prisca Foxburr of Loamsdown.