About 4 days ago I deleted about 20,000 pages of duplicate content off my ebay site. I don’t know how many of them google had indexed, but I can tell you that they sure hated them!!! Since the number of indexed pages had gone from 1500 to about 10,000, my traffic had gone from 150/day to about 80/day. Doesn’t make any sense…except that I’m sure google had indexed tons of pages that were almost exact duplicates of each other, but with different names. Since I got rid of them, the traffic has been greater each of the last 3 days, and yesterday it was at 150 again (these are unique hits).
Don’t have duplicate content on your site!!!