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I'd say you have a usability issue if those URLs are getting search traffic or direct traffic.
I'd say you need to change the page's content to show the out of stock nature of the product right away.
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.
Does all the content on the page remain the same except for the add to cart button?
Also, how long is the out of stock note relative to the rest of the text on the page?
[edited by: tedster at 10:07 am (utc) on Jun 14, 2012]
How about sitemaps? When a product goes out of stock do you exclude it from the sitemap as well as stop linking to it?
2. delete page and 301 to similar item
Can we assume that the "Join the wait list" message does not show up for products that have been unavailable for several years?
I would delete the item, which then shows a 404 page. You could then perhaps use keywords from the URL, to show related products which would improve the users experience.