I've just been contacted by a new client who wanted to know why his website no longer appears in Google, since about a month ago. I've done in-depth analysis of his Webmaster Tools account and there are NO manual penalties. His link profile looks more than fine, with no spammy inbound links. The only thing he says has changed is that he didn't pay his AdWords invoice for a month. The invoice has since been settled but since then his website actually does NOT appear in Google at all. If you search for site:domainname.com it comes back with no results.
Anyone else heard of this happening?