SEO help is required.?

[Dolan G]

I have had 306,000 product pages indexed in Google till July '07. From August, this month, Google started dropping our pages and the process is still continue. Currently we are left with 193,000 pages only. Although, we have approx. 600,000 products in our database. The website URL is http://www.smarterdeals.com. Its a Price Comparison Website and the product Feeds are refreshed by their respective vendors very frequently.NOTE: Sitemaps have already been submitted. Unfortunately, since the sitemaps have been submitted, the traffic started going down. Can anyone shed some light what's the reason behind it and what should I do in current scenario.