drupal_add_js() won't work with footer scope
Make sure you're printing $page_bottom in html.tpl.php. 

In Drupal 6, it looked like this:

&lt;?php print $closure; ?&gt;


In Drupal 7, you now want all 3 of the $page_top, $page, and $page_bottom variables which correlate to the header, content, and footer scopes. Here's a sample (and simple) html.tpl.php:

&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN"
  "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd"&gt;
&lt;body&gt;
  &lt;?php print $page_top; ?&gt;
  &lt;?php print $page; ?&gt;
  &lt;?php print $page_bottom; ?&gt;
&lt;/body&gt;
&lt;/html&gt;