I am clutching at straws somewhat but back in September my old established niche book selling website was badly hit after a Panda update. In August we had built a few individual country RSS feeds totaling about a 1000 book titles. On Google Webmaster I saw that the currency codes in the URLs were being seen as duplicate content and last month I programed a canonical link into then page heads to point at each books clean URL. (It's a dynamic php site.)
Our impressions on Google search are down to about a fifth of what they were previously. Has anyone seen anything similar with Google product feeds? How long does it take canonical links in the pages to be picked up by Google? Any help appreciated.