Recently, Google opened product AdWords ads all U.S. based advertisers and merchants. So now, if you use Google Merchant Center (aka Google Base), you can tie your AdWords account to it and show those fancy product images, pricing and so on, in your AdWords ads.
A WebmasterWorld thread has some advertisers a bit upset with the matching of the query, ad and the products actually displayed. Some are saying that the products being displayed for the query used is not showing the most relevant products.
Senior member, netmeg said, "Some of the products aren't matched properly (and I looked at some of my competitors, and theirs are even worse - lucky for me!)" A moderator, Buckworks, said "My AdWords rep said the system chooses which product to display based on parameters in the product's description but didn't say what those were and couldn't tell me how they could be tweaked."
Google did mention in their FAQs that you should use the new product extensions attributes to help Google better match the products in your feed to the query and your ads. Google said on that page:
To help us better match your Google Merchant products to search queries, you may attach one or more optional attributes to your Google Merchant Center offers.
Forum discussion at WebmasterWorld.