tedster - 2:28 am on Jun 14, 2012 (gmt 0)
I'd say you have a usability issue if those URLs are getting search traffic or direct traffic. Product churn can be a touchy area to deal with properly.
I'd say you need to change the page's content to show the out of stock nature of the product right away. If it's never coming back in stock, then link to a replacement product or remove the URL altogether (404 or 404 status) after a set time, may a few months depending the nature of the product. Definitely don't give the user a bad experience - and try to get one click whenever you can.
However, this is not likely to be a Panda issue IMO, unless you're repeating the exact same copy on all those out of stock pages. That might be deadly.