According to the post,
Official Google Webmaster Central Blog: New warnings feedback
Warnings allow Google to provide feedback on portions of your sitemap that may be confusing or inaccurate, while saving the real "error" alarm for problems that make your sitemap completely unreadable. Google hopes the additional information makes it even easier to share your sitemaps with them.
The new set of warnings includes many problems that we had previously classified as errors, including the "incorrect namespace" and "invalid date" examples shown in the screenshot above. We also crawl a sample of the URLs listed in your sitemap and report warnings if the Googlebot runs into any trouble with them. These warnings might suggest a widespread problem with your site that warrants further investigation, such as a stale sitemap or a misconfigured robots.txt file.
So if you have not done already, get an account on webmaster tools and improve your site so I can have good feeds on my feedotopia!