Google announced on the Google Webmaster Central blog that they will now send out notifications via Google Webmaster Tools for a spike in site crawl issues.
The warnings are called SiteNotice and are sent out when Google sees a significant increase in the number of crawl errors on a site. A crawl error can be when GoogleBot has issues access web pages. Sometimes this may be intentionally done by the Webmaster, but Google thinks it is a good idea to warn the webmaster anyway.
Here is a sample of the SiteNotice:
Now, if you don't log into Google Webmaster Tools daily or often enough, you can always use the forward to email feature, it does seem to work now.
Forum discussion at DigitalPoint Forums.