Automatically Link Twitter Usernames

If you want to automatically link twitter usernames, use the snippet below:

function snippet_twitter_replace($content) {
    $twtreplace = preg_replace('/([^a-zA-Z0-9-_&])@([0-9a-zA-Z_]+)/',"$1<a href="http://twitter.com/$2" target="_blank" rel="nofollow">@$2</a>",$content);
    return $twtreplace;
}

add_filter('the_content', 'snippet_twitter_replace');   
add_filter('comment_text', 'snippet_twitter_replace');

Twitter usernames in content and comments are being replaced. The username has to be something like @username.