If you have a significant other, do you have a private life?

In another question, I asked about whether people share their passwords with their significant others. Many people said they have nothing to hide, so they share everything (of that nature) with their spouse. This seems to imply that they really have no private life, any more, since they have nothing to hide from their SO.

I don’t know if I am taking things too far in interpreting what they are saying, but I want to question the idea that having a private life means you have something to hide. I think we all have private lives—and that this is a good thing. We are not totally merged with our spouses, and if we are, then there’s a kind of codependency that disturbs me. I’m not sure if that’s really the best way to be. Surely we all have thoughts that it would serve no good purpose to share with our spouses, although we may want to share them with other friends, or even write them down for our own good, but not for the eyes of anyone else.

So, do you share everything with your SO. Everything? Do you have no truly private thoughts at all? Do you believe that significant others should share absolutely everything? Is not sharing something hiding it? Is it your goal to have a relationship where you can share absolutely everything? Is a truly private portion of your self unnecessary or even undesirable?