From the law firm of Quinn Emanuel: "E-Mails and Discovery--Dealing With The Nightmare"--
Business litigators have by now learned that e-mail discovery is both a potential gold mine and a potential nightmare. Something about the medium causes people to make informal comments they would never dream of putting "on paper." And, people tend to be more cavalier about "destroying" e-mails relevant to litigation than they would paper. They just do not think of them as "documents."
The article goes on to discuss ways of persuading a judge that producing e-mails would be too burdensome. "If a judge can be made to understand why a request to retrieve old e-mail messages would make a company’s MIS personnel go pale with dread, the odds of that judge forcing the company to go to that effort will greatly decrease."