I have a sitemap file that has been submitted to Google, and has been processed, according to Google Webmaster Tools.
As per GWT for 2013-05-31, 8255 web-pages are submitted, but only 8209 are indexed.
Which 46 of the 8255 pages are not indexed?
ThompsonPaul wrote on moz.com about figuring out which pages are not indexed. Here is a summary of what he has to say:
site:search on Google. You can use a bookmarklet grab the search results into a list more easily.
Clearly this is a manual and time consuming task that isn't going to work well if you site has more than thousands of pages.