There's way too much overuse of e-mail in the workplace. And many managers are using e-mail for the ultimate no-no: reprimanding employees. That should only be done in person (or, if necessary, by phone).
E-mail is a wonderful tool for disseminating information quickly to a group of people. Unless it's absolutely necessary, though, make sure your one-on-one communication is in person.
Here's a typical story of how e-mail can be abused, and some good tips on preventing its improper use.