In the past twenty-four hours, it seems as if Google sent out a message to thousands, maybe hundreds of thousands, of site owners, that there is a problem with their site.
Typically, you never ever want to ignore a webmaster tools notification but in this case, the messages were sent in error.
Google told these webmasters that "Googlebot can't access your site", that the site had connection failures and Google was unable to access your site.
Here is a sample message one of my clients received (although I received several):
Google's Matt Cutts wrote in the thread that this seems like an error on Google's side. He said: