Maybe this announcement from Google has somethi g to do with it?

Hello,

Starting in late August 2010, we are making some changes to how your products in the Electronics, Books, and Media categories may appear on Google Product Search. In order to provide as much information as possible to our users, we need your help in matching your products to our "product pages" where users are able to view useful data such as product specifications or reviews. If you are submitting products in the above categories for the US version of Google Product Search, please start including unique product identifiers, such as MPN, Brand, UPC or ISBN. We will make similar changes to Product Search in the UK and Germany at a later date.

These attributes will not be required for your feed to process correctly, however, to avoid seeing a drop in traffic from Product Search, we urge you to start including these unique identifiers as soon as possible. You can find unique product identifier information on Product Search product pages, under the "technical specifications" section for Electronics items, the "Tracks" or "Details" section for Media, and the "Overview" section for books.

For more details, including what specific identifiers you should include for each category of item, please see our Help Center at http://www.google.com/support/mercha...?answer=160161

Sincerely,

The Google Product Search Team