As Product Manager for ChangeAuditor, I often hear about the difficulties with auditing Exchange (with native tools). One of the key things that people like about ChangeAuditor for Exchange is it's ability to capture non-owner mailbox access. While the tie in with Valentines day is tongue in cheek and intended to capture your attention, the ultimate question is one that's on a lot of people's minds: "Who can (or is) reading my e-mail... or accessing my mailbox?".\
As a user you expect that all permissions and privileges are setup properly so that only you can access your mail - all that personal and private (is there such a thing any more?) e-mail that you think only you have access to - and I'm not saying that isn't the case. But highly privileged accounts (like Exchange Administrators) have access to your e-mail (full disclosure - they need access to properly administer your mailbox). There should be a reason for this access - and if you're not tracking the access, you'd never know. You'd merrily go on about your emailing ways.
As I hinted above, Exchange can audit this non-owner mailbox access (see this link to configure it for Exchange on-line...but be warned, it's on a per-mailbox basis, so you'll either have to write a nice powershell script, or do them one at a time: http://help.outlook.com/en-us/140/ms.exch.ecp.auditingreportshomelearnmore.aspx). Wouldn't it be nice if it were all centralized for you? Wouldn't it be great if you could see an alert when someone tried to access your account - and whether they were successful or not? ChangeAuditor can help you here. With alerting to the mailbox owner (and others like Exchange Administrators, if desired), you'd feel a lot more confident that you'd know when someone was trying to access your e-mail. You don't have to worry about Exchange Audit logging and the space they consume. You don't have to rely on the Exchange administrator to run reports that they may have an interest in you not seeing.
So if you want your love letters to remain private - or at least be told when someone else is reading them - look into auditing non-owner mailbox access and get alerts set up to tell you about all your fans