Recently a large amount of users got an email from Google Webmaster Tools with this subject: "Googlebot can't access your site".
Inside that email there are some other details, such as the number of errors that Google encountered while attempting to connect to your site, as well as your site's overall connection failure rate.
If you judge by that email message and the failure rate ratio, you could think that your business is ruined given that people are saying a failure rate above 50% and sometimes even around 75%.
The good news is that this appears to have been due to a bug in the Google Webmaster Services.
There is a forum thread going for it on the Google product forums at:
(click this link and look on page 1)
According to Matt Cutts at Google, these should be ignored for now.
For safety reasons you may like to ask your hosting support to check what was wrong with the server, if there was something wrong at all.
They could check the server access logs and see if there were any "unusual" errors for the Google bot traffic to the site.
Hope it helps!