We just got bit by this recently. One day our organic referrals just took a nosedive (4000 -> 1000 clicks/day overnight). We got in touch with our Adwords contact, who said they'd look into it, then ... left. No longer with the team. Now we have no contact and no way to figure out what went wrong and how we can fix it.
It didn't have a huge impact on us, but it did cost us ~$3k/month, which isn't negligible. The worst part is that there's seemingly no way for us to address this, despite spending a pretty significant amount of money on Adwords every month.