How to display a block to a specific user?
I would implement hook_block_view_alter() and remove the block's content when the uid is not the user you were aiming at. In this example we only show the block content for uid 2.

function hook_block_view_alter(&amp;$data, $block) {   

   if ($block-&gt;module == 'somemMdule' &amp;&amp; $block-&gt;delta == 'someDelta') {
         global $user;

    if ($user-&gt;uid != 2) {
       $data['content'] = array();
    }
  }
}