It’s likely that retailers will see a large dip in traffic to their websites if they have been reliant on Google Shopping for traffic. You’ll also want to monitor your AdWords as they too may get less clicks as Product Listing Ads start to appear mixed with search results.
The change is scheduled phased in, but to be complete by the end of the second quarter of 2013. Product Listing Ads are being introduced in the United Kingdom, France, Japan, Italy, Spain, Netherlands, Brazil, Australia and Switzerland and have been live in the US since October 2012.
If you want to find out more, then Lengow have produced a PDF guide to Product Listing Ads to get you started (which is worth reading even if you don’t currently use Lengow to manage your feeds). It covers the basics as well as the things you need to know such as the new layout you’ll need to use for your Google feed.