Activation Email for Pending User Doesn't Work
After following the stack trace for activating a user (with the link), I discovered that activation fails at /craft/app/services/UsersService.php:822:

820:   public function verifyEmailForUser(UserModel $user)
821:   {
822:      if ($user-&gt;unverifiedEmail)
823:      {


Apparently I needed to set the unverifiedEmail property when creating "Pending" users via a plugin as opposed to only setting the 'pending' property to false.

$user = new UserModel();
$user-&gt;email = 'pendinguser@email.com;
// ... set other properties
$user-&gt;pending = false;
$user-&gt;unverifiedEmail = '';