Greg Olson from videomaker recently published a very important video on copyrighting your videos (this also applies to music etc.). The laws are actually more simpler than you might think and what you need to know (and do) is also not too complicated.
The bottom line is this. When you are talking about the U.S. (and each country has its own set of laws) creating an original video and publishing it online should make it copyrighted. However if you will ever find yourself in court trying to prove that somebody violated your copyright it will be in your best interest to register in order to make it official on the copyright.goc website (thee fee is $35 for doing so online using the electronic Copyright
Office or eCO).
At the end of the day, we are not lawyers (and nighter is Olson) so take every advice here for what it is, read the copyright.gov Q&A – its pretty strightforward (for a goverment document) and if you simply must – talk to a proffesional.
We have a full section devoted to everything that has to do with being a professional photographer/videographer called “photography as a business” here on LensVid.