Well we've had a thread on John's marriage to Cynthia which is not nearly so hot an issue as his relationship and marriage to Yoko.
John wrote endless songs about their relationship, they talked about it in interviews.John and Yoko marketed themselves as inseparable soul mates, but they had an 18 month separation and by the sound of it they spent long periods apart after they got back together, interesting to contrast with Paul and Linda who didn't seem to make so much of a public statement about their relationship but almost never spent a day apart.
Yoko is definitely an interesting figure, she has some talent and a lot of nerve, she's sassy for sure. But I'm not greatly excited by her art and think her influence on john's was for the worse, I've mentioned this elsewhere, the idea that you've got to write about yourself is not an artistic credo I share and although john tried to review his Beatle work in that light I think his work with the Beatles shows rather the idea that you could write a song about anything, mixing personal with popular culture, circus posters, lewis Carrol, childs art, the book of the dead, newspaper articles, advertisements, tv sitcoms whatever.
Greg supplied the following link to a fascinating discussion on Yoko here:
http://somethingaboutthebeatles.com/44-oh-yoko-or-all-i-want-is-the-truth/I don't want to dump on Yoko but I think there has now been a reaction against some of the hatred that initially went Yoko's way for "breaking up the Beatles" and now people think that was completely irrational and she was an innocent victim who never knew how rich and famous the boy she was getting into a relationship was and it was all so innocent and romantic, even the heroin addictions.