Search engine spiders don’t like Javascript - in fact they just won’t execute it. That’s a problem for people who have their content served by fancy Web 2.0 AJAX-based sites - the search engine spiders just can’t see the content, so it doesn’t get indexed. This session went over what your options are to avoid that problem.

If you use negative z-index values in your CSS it will work properly in Internet Explorer and Safari, but you’ll have problems in Firefox.