For anyone with a mobile-enabled site, you can now add a Mobile Sitemap. More info here:

Mobile Sitemaps:
https://www.google.com/webmasters/sitemaps/docs/en/mobile.html

Submitting your Google mobile Sitemaps:
https://www.google.com/webmasters/sitemaps/docs/en/submit_mobile.html

(The pages say they were last modified on 16 August 2005, but I've only just seen the link on my Google Sitemaps account page today.)

There also appears to be a new "stats" feature too. In order to view some stats for each site, you have to "verify" your sitemap to ensure you are the owner. This is done by placing a file in the root of your domain.(The "random" name of which is given to you by Google when you click the "verify" link.)

The stats show which files from your site Google has had problems indexing. This is shown for pages from your sitemap *and* pages found during its normal crawl, giving reasons for each one.