It's funny because I know a woman who is named Ono Yoko (Yoko Ono in western name order).
Most people that I've talked to about this (who are Japanese) don't really know who she is. Some people know a little bit, but not enough to like her or dislike her. Some people strangely like her. And some people dislike her just because they know that people dislike her (like beatles fans from England or the US for example).
I've even met a singer who dislikes Yoko Ono simply because she married John Lennon (instead of the singer, of course... it was funny because she felt that she almost had it since she is Japanese like Yoko Ono).
My wife didn't even know who she was. So we did a little bit of research. In fact, there is a documentary about her on youtube--
YouTube - The Real Yoko Ono (Part 1 of 6) 素顔のジョン&ヨーコ
I don't know how much of it is truth, but it was entertaining nonetheless. It is in English and has Japanese subtitles.
I know that there is a lot of info about Yoko Ono and John Lennon on the internet... and not knowing either one of them personally I have no idea what is truth and what is not. I think that John Lennon certainly made a choice as a man to be with her-- so a lot of the blame that gets put on her seems to be a little unfair. Just in case you're not familiar with the situation, a lot of Beatles fans blame her for the break up of the Beatles. I personally think it was more than that (particularly their manager's (Brian Epstein) death. She certainly didn't help the situation though. As Ghap said this is an argument that has and will go on forever.
Personally, I don't like a lot of her music... but I think it's interesting to note that the two of them made some very experimental music that I guess could be classified as 'noise rock' or 'noise' or whatever they call it now days. While I think her musical contributions had no place within the Beatles, out of context there was some interesting stuff here or there (although I can't stress enough that I don't like it).