We are in the beginning stages of implementing Personal Archive Mailboxes for our users. Currently we have a small group of testers using them. We like it fine but have noticed some gotchas such as no support for any mail client on Mac and searching on OWA is a two step process.
We are considering going ahead anyway but would like to have a contingency plan just in case some people decide to opt-in but later decide that they want to opt out.
What comes to my mind now is that if they want to opt out the mail box gets moved into a database that has a very long archive policy and then they are given a timeframe within which they will have to move their mail back into their regular mailbox.
I am looking for better suggestions.