Review of The Post-Birthday World

I just finished reading The Post-Birthday World by Lionel Shriver. My first impression is that this male author seems to know a lot about how women think, which is so unusual.
The book has two alternative worlds for Irina, depending on whether she succumbs to the temptation to kiss a friend on his birthday or whether she resists because of her significant other who is out of town. The chapters alternate between the two different worlds and contain some parallels.

The themes include growing older, what is love, relationships with mothers and sisters, excitement vs. companionship, American vs. Brit and others. The interesting thing is to see how her decision changes everything. Irina is a children's book illustrator and she uses her experiences to author and illustrate two children's books (one for each parallel world). The books also reflect some of the same themes as the novel.

The author has cleverly written the dialogue and does a great job of giving the reader the feel for a British lower-class accent and idioms. Some of the parts seem to be too detailed and it drags a little, but then the next chapter switches to the other life so there is variety.
I would recommend this novel, especially for someone who has made a relationship decision and always wonders whether it was the right choice.
Has anyone else read this novel?