Secrets can become a cancer in a marriage. The affair was born and thrived in secrecy.
Somebody who has nothing to hide will not object to sharing email/phone passwords, etc. Transparency means being open so that the betrayed spouse can rebuild trust. A transparency plan is something you establish in the hopes of rebuilding that trust: access to email, facebook, phone accounts. Not tollerting hiding where they go and what they do.
If you are taking a spouse back, what is your transparency plan? If you don't have one, there's a good chance you really will turn into an interrogating cop, always asking questions. It's much easier to have access to accounts and such and have them tell you--honestly--about what they did in a given day without having to pry it out of them.
M-47,W-40,No kids D-filed 5/27/2010 Piecing - 10/21/2010 -=Soon to be banned=-