Drupal 7 now has an option to use the site name (i.e. the value of the site_name variable) as the "Display Name" in the From header in system e-mails. For example this would mean the sender might be "Acme Website" <[email protected]> as opposed to just the e-mail address alone. In order to avoid disruption, this is not enabled by default for existing sites. New sites will have it enabled...