Server failures happen, they are almost guaranteed. And when they do happen, SEOs hope that Google does not try to visit the site during that timeframe. If Google does and the server issues are database related, then Google may index your site and use "Cannot connect to database" or something related as your page title and meta description.
And the page might look like this in Google's cache.
That is the problem one member wrote about at this DigitalPoint Forums thread. This member explained that he did not have any redundancy, so his error message returned that error:
So Im currently on Page 1 of google (P8) for a 'fairly' competitive term (15mill results) and its indexed my site as 'sitename' cannot connect to database - its also used my keyword anchor text for the page title.
I assume Google will come back relatively soon and reindex the page. Once Google crawls and reindexes the page, it is only a matter of time for the Google search result to revert back to its old self again.
Forum discussion at DigitalPoint Forums.