I'm an open book. My hubs knows the passwords to all of my stuff (I only have three password variations, so he could get into anything anytime.) I doubt that he's ever looked, but it wouldn't matter to me if he did. I tell him everything anyway.
Hubs needs his privacy, which I was always respectful of-- until the whole dishonesty, trust violations, lying thing came into the picture. And then that privacy became an issue to me because by respecting his privacy I allowed the space for him to lie to me.
I can totally see where Mohegan is coming from.. in that after that trust has been broken having the ability to see whatever you feel you need to for a while can really speed the healing process. Because your partner has then understood how much they've damaged the relationship and trust, and is willing to work through the process of showing you everything so that you can trust they are telling you the truth, and you can get to trusting them again much faster. I see that as more of a temporary process, though, hopefully getting to the point where it's no longer necessary.
I didn't have that open book with hubs, and we've gotten to a good place, but it took YEARS because I didn't trust him again after that, not fully. I didn't think he was lying all of the time or even a LOT, but because I had no way to know either way I got to the point where every single thing he said I took "with a grain of salt", as in-- could be the truth, maybe not, whatever. I can't tell you how much that destroys intimacy and caring for your partner when nothing they say to you really matters anymore. We've moved past it, but it was much harder and took a lot of time.
I DO understand the feeling that when he has a partner, she might not want everything she says passed on to me, and vice versa. That's dealing with a third person's privacy and that can get sticky, especially when there are so many people involved, what if that person tells you something that your partner really SHOULD know? I've never been there, so I don't know, but it does seem that you have to really consider each case individually.
Sometimes I think I need a separate private side of myself. I'm just not sure I am capable of that.