As I mentioned previously and in my latest book, data mining your corporate email can yield some pretty interesting information... even if you don't read the contents. My angle is that by analyzing who emails whom and when, you can get a sense of who is "friends" with whom... and by doing so you can hit the ground running with any Enterprise 2.0 social software initiatives.
One nugget that I never thought of was how the emergence of email "cliques" can determine whether or not your company is in serious trouble... Two researchers -- Ben Collingsworth and Ronaldo Menezes -- recently analyzed the email patters at Enron to see if there were any predictors of the impending doom. Initially, they thought they would find interesting changes immediately prior to a large crisis... However, what they found was that the biggest change in email patterns happened one full month prior to the crisis!
For example, the number of active email cliques, defined as groups in which every member has had direct email contact with every other member, jumped from 100 to almost 800 around a month before the December 2001 collapse. Messages were also increasingly exchanged within these groups and not shared with other employees... Menezes thinks he and Collingsworth may have identified a characteristic change that occurs as stress builds within a company: employees start talking directly to people they feel comfortable with, and stop sharing information more widely [prior to a crisis].
Interesting stuff... although this is only one data point. The increase of "active email cliques" is probably a good indicator of the amount of stress and negative rumors in your company, or in a specific division. However, as an actual predictor, it might not work so well. It will be difficult to know for sure, because its really difficult for researchers to get access to random corporate emails.
Also, if you institute any kind of email data mining system, people will alter their behavior. These email cliques will simply go offline if think that big brother is watching... they will probably leave some kind of a trail, but it will be more subtle, and lead to lots of false positives.
Ultimately, as a manager you're probably better off just talking with your employees to see if they are demoralized... because spying on them might only make matters worse.
(Hat Tip: Nat Torkington)