I'm having exactly the same problem. It also started on 14th April 2012, bounce rates going up, new visits also, shortening Time on site and lowering pages per visit...
Pageviews remain the same, which means that for some reason, users are 'losing' __utma cookie, responsible for tracking the user as unique.
One thing I found interesting through GA - in my case this problem does not show for Opera 11.64. It holds its previous value of about 14% bounce rate. Other browsers (mainly new versions of Firefox and Chrome) went through the roof (bounce rate of 65-90%).
I am talking about a website with couple of hundreds of thousands of visits...
Tommorow I will try change a few things, and post back if I find anything useful.
UPDATE
I have updated the code to the new one
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'XX-XXXXXXXX-X']);
_gaq.push(['_setDomainName', 'example.com']);
_gaq.push(['_trackPageview']);
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
</script>
instead of the old one
<script type="text/javascript">
var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");
document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
</script>
<script type="text/javascript">
try {
var pageTracker = _gat._getTracker("XX-XXXXXXXX-X");
pageTracker._setDomainName(".example.com");
pageTracker._trackPageview();
} catch(err) {}</script>
The difference in _setDomainName
is that in new code it doesn't have the leading dot(.) in domain name, and there seems to be the problem with the old code.
I must add that I'm not having any trouble with the other website that doesn't have _setDomainName
part, and still is running the old code.
I also found a blog post about the same problem:
http://diegoscataglini.com/2010/08/17/118/google-analytics-setdomain-beware/
Anyway, now things are back to normal. Bounce rate back to 11%, time on site going up as well as Pages / Visit.
When you change the code cookies will be recreated for all users, making them new visitors coming directly to your site. In a day or two (depending on number of visits), as people use your site as they do normally, statistics go back to normal.
I had to wait couple of days before reporting back, and I hope this will solve your problem too.