The Google Webmaster Central team posted a known issue report with a bug in the reporting engine within Google Webmaster Tools. The indexed URLs report is currently showing 0 pages indexed for most sites who have submitted sitemaps to Google Webmaster Tools.
The notice reads:
The indexed URL counts for Sitemaps that you have submitted in Webmaster Tools may be showing zero (0) indexed URLs for some sites. We are aware of this issue and are looking into it; you do not need to take any action. This will have no effect on your site’s performance in search results.
That being said, many webmasters are unaware that this is a wide-spread issue. There are hundreds of webmasters resubmitting their sitemap files or trying to fix an issue that does not exist with their sitemaps files. I have linked to these reports at the Search Engine Roundtable.
Best advice is to sit tight and wait it out.
Postscript: JohnMu from Google commented at about 4pm (EST) that this should now be resolved. I personally see my sitemaps showing the proper index count. John said:
For what it’s worth, this should be resolved now. It may take a bit for the data to propagate to all accounts; you can speed that up by resubmitting your Sitemap file in Webmaster Tools.