How does iPhoto synchronize photos between my macbook pro and my wife's one? When my wife imports photos on her mac book pro, they are quickly synchronized in my own iPhoto. 

We share the same apple id, but I do not remember having set anything specific to have this (excellent) behavior. How does it work ? (that means : what is the setting to obtain this behavior ?)
There are two possible answers here:


You are both sharing the same iCloud/.me/.mac account. Look in System Preferences > iCloud > [Account Details] on both systems to compare.
That your wife has shared a Photo Stream with you. Run iPhoto and look at the left hand sidebar in the section named 'Shared'.