Wow, I actually require girlfriends, wives and other others to give me access to email, cell phones and other electronic data. any kind of chat logs, etc.
I think it's perfectly normal and acceptable. I even had one girl install a keylogger so I could see every letter, number or shift key. I also had an audio recorder installed and running any time her computer was on so she couldn't circumvent text logging with audio. Maybe some people think that's inappropriate somehow, but no woman has ever told me it made them uncomfortable or paranoid or anything like that.
On the other hand, I would NEVER let anyone see my text messages or pm logs.....EVER.