Broken Links

Although it can be somewhat of a nightmare to implement, the best strategy is actually to recreate those URLs and make them "301 Permanent Redirects" to the new pages. You can start with some of your main products and categories.

301 Permament Redirects are the "search engine optimized" way to tell a search engine that the page permanently moved to a new location. In Google terms, this means that the PageRank of the old page should be transferred to the new one.

This strategy also provides another important result: any links that point to those products and categories will not end up in a "404 Page Not Found Error", but rather will be redirected to the correct page.

Of course, here we are referring to links that you have no control on. Some of those links might have been "powerful" back-links that were giving significant PageRank to your store pages. If those links now return a 404 error, they will lose their effectiveness, and you definitely don't want that to happen. You need all of the back-links to your Web site to remain relevant. As you probably know, you can query Goole for a list of back-links and see which pages they point to: those are the first pages that you need to address.

This article in the Google Webmaster Center covers your scenario and talks about 301 Redirects.

We hope this helps and thanks for the kind words about ProductCart!

You might be able to discover some of those old links by typing in Google search box exactly this (with your domain name):

site:www.yourdomain.com

It may not be too late to see what Google has retained.