Today means nothing. Even if you are an extremist right-wing fundamentalist who likes to run up and throw Bibles at people, you can relax. The world ain't ending today.
The concept of 666 being evil comes from the book of Revelation in the Bible, where it says that the devil places a mark on the right hand or forehead of all but the servants of God.
That mark - 666 - is generally considered to be Hebrew numerology (gematria - assigning numerical instead of phonetic value to each letter of the Hebrew alphabet). 666 means "Nero Caesar" who was responsible for the widespread persecution of Christians and Jews.
So relax, skip church today, and keep praying to that idol you call "the golden arches". It's all okay.