There are other options in between doing nothing and registering at the copyright office. You actually are the copyright owner of your original work without you doing anything, but you must be able to prove this; once your work has been put out "in the wild" on the internet, not only can you have your content stolen, but to add insult to injury you can be accused of being the thief!!
You can send yourself a cd in a sealed registered post envelope.
There are online options too; I like www.digiprove.com because they use digital fingerprinting (you don't have to upload your work); it's an industrial strength product but there is a free starter pack.