I've been a fan of Google Sitemaps since their initial release last year. For myself, I felt that the true benefit of Google Sitemaps would be to provide insight as to various potential indexing issues with my client's sites. However in the 'early days' of Google Sitemaps, there was no real data to help me determine if there were indexing issues with the sites that I submitted.
In early May I was pleased to see the improvements that were made to Google Sitemaps. They made it easier to submit, they provided more statistics and they even implemented a Summary Page to let Webmasters know if their site is being penalized through what they call the Notification of violations of the Webmaster guidelines. This week, Google Engineer, Vanessa Fox announced some new features with the latest release of Google Sitemaps.