I run a free classifieds website http://www.jihoy.com, and was ranking fairly well from some of the competitive keywords. Then I found a few people who were literally posting the same ads, like 10 times or more, with very little variations. So I went and deleted about 200+ pages. I figured that wouldn't matter much since I have about 25000+ pages. Then I see traffic from Google get cut in half! I am not sure what I am doing wrong exactly. It's only 1% of my content, and non of those pages have page rank. Maybe Googlebot is confused? I am not going to delete anyt duplicates anymore, not until I get ranked again for my keywords.
Sounds like quite a lot of pages to delete all at once. Were any of these pages the ones that were previously ranking? Have you submitted a new sitemap to Google? Have you ensured that when these were deleted there were no broken links? Just some ideas
Maybe, some of the pages you deleted have some good spot in google search results. It is ok to delete pages, but next time, try to check with your google.com/analytics and google webmaster tool on pages that you don't have traffic before deleting. Avoid deleting high traffic referred pages.