Pjman - 10:55 pm on Oct 8, 2012 (gmt 0)
The DNS warnings are messages in google's webmaster tools. The just say g bot was unable to connect to your site.
The are pointed out in you messages section. I got one 2 days ago. My infrastructure never noticed any errors though. I monitor with 3 independent source all saw no change in performance at all 3 days before and after the Dns warning period.