The change log says:
This version only partially satisfies the new requirements set out by Google which will come into effect on September 22nd, 2011. In particular, all of the variant attributes for apparel are not yet supported. To prepare for the next update, begin making "read-only" attributes in your Zen Cart admin and set the option name to the name of the variant attribute (i.e. Age Group, Material, Size, Color, Pattern, Gender, etc). The final version of our module will require Stock by Attributes (SBA) to be installed and stock IDs to be created for each of the product variations that you offer. A bug in SBA prevents us from moving forward with this plan due to the fact that read-only attributes cannot be used with SBA. We are working on our own version of SBA which we will continue to support through the Numinix.com website as soon as it is ready, The Google Merchant Center Feeder will automatically begin using these attributes.
However, if you set up these attributes to NOT be read-only and create stock IDs for all of your combinations including these attributes, GMCF will automatically begin using them in version 1.10.2.