PIE fails until the official demo page is visited..
Ok this is a strange one. I've been testing CSS PIE out, and had a range of things working quite nicely.
Then out-of-the-blue all of the PIE effects starting failing.
After going around in circles for 30 minutes I thought I'd double check that your demo page was still working (http://css3pie.com/demos/tabs/
It was, and then when I reloaded my local test page, that miraculously started working again.
Strange, or what?