As recently as yesterday, people on TrekBBS were arguing over whether or not Leonard Nimoy and William Shatner should appear in the next nuTrek movie, as a homage to the 50th anniversary (the movie is scheduled for release in 2016).
Well, that's moot now.
Personally, I didn't think he had much longer to live, given how seriously ill he had been. So while I've been sad all day, this wasn't really a shock. All I can say is condolences to his family and friends, and that we are the poorer for his passing.
I became a Star Trek fan in 1975, at age 12. Almost from the get-go, Spock was my favorite character and Leonard Nimoy edged past Michael Douglas in my personal category of "favorite actor." Over the years I've seen many more of his performances than just what he did that was Star Trek-related, and came to appreciate his dedication to excellence.
One of the things I read on a Star Trek forum, of all places, is that now that Nimoy has died, "Star Trek has died." Well, no, it hasn't. The actors are mortal, but hopefully the positive ideas and hopes raised in ST will never be mortal. So many people have been inspired to excel in their chosen careers and hobbies by this show, and that couldn't have happened without the actors giving credible performances. Leonard Nimoy has left his mark on this world, and it's a good one.