re: FlatRateShippingAdjustment
look fine for me. This is a class defined in the Google API - be sure you have a valid reference to the GCheckout.dll
re: correct the code to maybe pass the type/object for the shipping by weight table definition
I'm not sure what you mean. The bottom line is that currently the Google Checkout plugin can only use flat rate shipping. This is because clicking the Google Checkout button goes directly to Google - i.e. it does not let the customer choose a shipping address. All the non-Flat Rate methods require a shipping address (whether they be By Weight or external carriers like FedEx).