The explosion in spam and e-mail virusses (and the problem of information overload generally) has led to increasing negativity around the usefulness of e-mail, with many commentators suggesting that e-mail is about to be replaced by less easily abused technologies such as RSS syndication. E-mail also doesn't have a very good name as a collaboration tool for anything larger than two-person groups.
However, John Udell (2003) argues that e-mail is in fact in some ways an excellent platform for group collaboration:
Every interpersonal e-mail message creates, or sustains, or alters the membership of a group. It happens so naturally that we don't even think about it. When you're writing a message to Sally, you cc: Joe and Beth. Joe adds Mark to the cc: list on his reply. You and Sally work for one department of your company, Joe for another, Beth is a customer, and Mark is an outside contractor. These subtle and spontaneous acts of group formation and adjustments of group membership are the source of e-mail's special power. Without any help from an administrator, we transcend the boundaries not only of time and space but also of organizational trust.
An ad-hoc group convened by e-mail dissolves unless membership is reaffirmed by each message. This is a feature, not a bug. Many of the groups that perform work in a modern organization are transient. A hallway conversation is over in minutes; a spontaneous collaboration can last a day; a project may take a week. Software that requires people to explicitly declare the formation of these groups, and to acknowledge their dissolution, is too blunt an instrument for such ephemeral social interaction.
Among communication technologies e-mail probably also has the second lowest 'entry threshold', after telephones, in terms of pervasiveness and ease of use.