Google is now inviting webmasters to try out the new Webmaster Tools structured data error reports.
I signed up for the beta a few weeks ago and was invited yesterday to check out the reports. Fortunately for me, but unfortunately for you, I have no errors - so there is not much to show you.
However, I did spot Tony McCreath post screen shots with errors on Google+ for all to see.
Here is the screen shot showing the more detailed errors coming to your structured data report within Google Webmaster Tools:
Tony said that this report has been helpful to him, he said so far "it's highlighted a couple of issues that I would probably never have found without it." "So very happy," he added.
Forum discussion at Google+.