On my weekly check of our webmaster tools I noticed that alot of the sitemaps show that the URLs are submitted, but that none of the URLSs show to be indexed.
Upon further investigation I noticed that the sitemap sections that appear as not being indexed are the same sections we submitted to google base/google merchant center.
Just a little background: We started submitting data feeds to Google Merchant Center approximately 1 month ago. We've had our WMT account for several years, we are an ecommerce site and totally white hat. We've noticed a 10% drop in traffic over the last two weeks.