WP_query exclude posts of a format

Question

tax_query takes an array of arrays. Try this:

$myposts = new WP_Query(array(
                'tax_query' => array(
                    array(
                        'taxonomy' => 'post_format',
                        'field' => 'slug',
                        'terms' => array('post-format-quote'),
                        'operator' => 'NOT IN'
                    )
                ),
                'posts_per_page' => 3
                )
            );

Further reading: http://ottopress.com/2010/wordpress-3-1-advanced-taxonomy-queries/