[Steven Zahm]

@ Heather

Well… someone edited a core WordPress file on your site:
../wp-includes/query.php

It was this:

function get_query_var( $var, $default = '' ) {
    global $wp_query;

/*  return $wp_query->get( $var, $default ); */
}

And it should be this:

function get_query_var( $var, $default = '' ) {
    global $wp_query;

    return $wp_query->get( $var, $default );
}

The return was commented out so it would not return values like it should. Not sure why this would be done, but it can definitely breaks things pretty badly.