In most of the world 1 January is the day that copyrights expire and previously monopolized content enters the public domain. The one exception is the USA, becuase every time it looks a copyright might expire Congress is bribed into adding more years.
So when was the last Public Domain Day here in the USA? I'm not sure, but I beleive it was in 1992. You see, anything created in 1964 or after will be under copyright for quite some time, and anything published before 1964 would only be in the public domain if someone forgot to file for an extension to the original 28 year term.
Pardon me for focusing on the USA, but for most of the world it's just another holiday. For Americans it's a reminder that we got screwed by Big Media.
How do you plan to celebrate the day?I haven't decided yet, myself.
P.S. Don't ask what "original 28 year term" means. Trust me, you'll be happier not knowing. US copyright law is incredibly complicated.