On September 14, 2010, Bergen County Assignment Judge Peter E. Doyne issued a written opinion in North Jersey Media Group v. Bergen County Economic Development Corporation, Docket No. BER-L-6593-10. That opinion is available for download here.
The opinion, while "unpublished" (i.e. it creates no binding precedent), is very instructive, especially on the question of whether a public agency is legally required to establish a system to properly preserve e-mail records.
Judge Doyne ruled that the Destruction of Public Records Law doesn't create a private cause of action (i.e. a citizen cannot seek a civil penalty against a government agency or official who loses or destroys a record). But, he also ruled that since the defendant agency "has no guidelines for the retention of records" it shall "implement a policy to maintain and preserve records required by statutes and regulations."
Based on Judge Doyne's ruling, I believe that it is at least arguable that public agencies are under a ministerial duty to design a system that collects and archives official e-mails. Thus, if a citizen knows that municipal council members are sending and receiving official e-mails from their Yahoo, AOL, or GMail accounts and that there is no municipal policy requiring those e-mails to be preserved on the municipal server, I believe that citizen may be able to successfully bring an action in lieu of prerogative writs to compel the municipality to implement to establish such a policy. (For information on compelling a government agency or official to complete a ministerial task, see my blog entry "My town won't obey the law. What do I do?")