I guess I am not the josei type, cuz I did not like this manga too much. I heard, and read so many nice reviews about this... I even bought the anime, so I was eager to read the manga. Sadly, it was MEH to me.
There are two Nana in this story: one of them is a naive, silly girl who fells in love with any handsome man she meets, and the result is that she keeps getting her heart broken. The other Nana is a rocker girl, not naive, tougher in looks, but in reality, had her heart broken because her boyfriend moved out to Tokyo. So both Nana have different aspects, but their stories are pretty much the same.
So far they did not meet yet... I guess the real thing starts to happen when they do and become friends. I do not know and i think I will never do.