@ed10: thanks for the info.
Since the users.email field is not being used anywhere in the code if acquired using get_user_by_login() (as is done here in line 81 of includes/current_user.inc), the following patch will ensure it's availability in any script that uses it:
--- old/includes/current_user.inc Thu Jan 17 19:16:02 2013
+++ new/includes/current_user.inc Mon Feb 04 05:42:49 2013
@@ -22,6 +22,7 @@
var $loginname;
var $username;
var $name;
+ var $email;
var $company; // user's company
var $pos;
var $access;
@@ -120,6 +121,7 @@
$this->username = $this->loginname;
$this->prefs = new user_prefs($myrow);
$this->user = @$myrow["id"];
+ $this->email = @$myrow["email"];
update_user_visitdate($this->username);
$this->logged = true;
$this->last_act = time();