Are there any downsides to prefetching webpages using javascript?

Question

I'm currently experimenting with prefetching pages to increase perceived performance of our website, using the code below (req. jQuery).

Only 0.5% of our visitors use dial-up, I'm excluding querystrings (good old times), externals links (http) and pdfs (our large files are in this format). On a production site, what other possible negative scenario's apply when prefetching that I haven't considered?

<script type="text/javascript">
$(document).ready(function() {
$("a").each(
function(){
    $(this).bind ("mouseover", function() {
        var href=$(this).attr('href');
        if (
            (href.indexOf('?') == -1)&&
            (href.indexOf('http:') ==-1)&&
            ($(this).hasClass('nopreload') == false)&&
            (href.indexOf('.pdf') == -1)
        ) {
            $.ajax({ url:href, cache:true, dataType:"text" });
        }
    });
    $(this).bind ("mousedown", function(btn) {
        if (btn.which==1) {
            var href=$(this).attr('href');
            if ($(this).hasClass('nopreload') == false) {
                window.location.href = href;
                return false;
            }
        }
    });
});
});
</script>

For certain links, when hovered over it will preload the page and on mousedown will navigate (rather then after the button is released).

Answer 1

A right click will trigger a mouse down event too - so you might want to check the events data.

I guess that the speed gain for html source of 20-30kb is rather low. Your function does not preload any image, css or js files but only the pure html code.