Having met Shatner, well I use meeting in it's loosest sense, I can confirm that he is indeed a rude and arrogant arsehole.
I can quite understand why the original Trek cast despised him, and those who are still alive, still loathe him. Only Nimoy will talk to him.
Based on what I have seen and heard, Leonard Nimoy comes across as a kind and intelligent gentleman.
George Takei is also lovely with fans. I met him last year and he's a delight - very charming and funny!
It's a real shame about Shanter. He's got one of the worst reputations I've seen for being a total git but his behavior toward his fans seems so unnecessary and almost cruel. There are so many actors who would kill to be so fondly remembered years after their career peaked.