In the series of books (and the radio series before) the main protagonist, Arthur Dent takes a very confused and confusing journey through both the time and space of the universe, all the while wondering why the answer to "life, the universe and everything" was 42.
On just one occasion has Douglas Adams offered an explanation for the number 42 as the answer to the famous question. "The answer to this is very simple. It was a joke. It had to be a number, an ordinary, smallish number, and I chose that one. Binary representations, base thirteen, Tibetan monks are all complete nonsense. I sat at my desk, stared into the garden and thought '42 will do' I typed it out. End of story."
There are plenty of alternate explanations, amongst which an amusing (and probably post facto) suggestion comes from the Encylopedia Uslessia where The series ends with the destruction of Arthur and all possible Earths by the Guide. In the final pages of Mostly Harmless Arthur enters Stavros Mueller's club Beta and all of the twisting storylines come to a very final conclusion. The street number of the club is #42; this leads to the possibility that the Question of Life, the Universe, and Everything is: "Where does it all End?"
However, let's return to the theme at hand.
And also recall a portion of Adams' comment on the previous page. "Binary representations, base thirteen, Tibetan monks are all complete nonsense."
Forget the base thirteen and the monks, just consider the binary part. And take note of today's date.
Today is 10/10/10 - a date that will only occur once every century; hence the major significance; it's not an annual event like Star Wars Day or Halloween.
So, take out your scientific calculator and convert 101010 from binary to decimal to be sure of the significance of this day.
To all fans of Douglas Adams, enjoy the day; perhaps even post a comment on Twitter to voice your support.