Google is now sharing more detailed Site Error info in Webmaster Tools. Sire Errors will now display stats for each site-wide crawl error from the past ninety days. It will also show failure rates for category-specific errors.
"This information is useful when looking for the source of your Site Errors," Google says in a blog post. "For example, if your site suffers from server connectivity problems, your server may simply be misconfigured; then again, it could also be completely unavailable! Since each Site Error (DNS, server connectivity, and robots.txt fetch) is comprised of several unique issues, we’ve broken down each category into more specific errors to provide you with a better analysis of your site’s health."
Users can hover over any of the entries in the legend to get an explanation of the errors. When you do so, there will be a "more info" link.
Google recently added alerts for Search Queries data in Webmaster Tools, as well.