In my experience...
I've seen a number of sites getting the Google CAPTCHA message and the cause is almost always someone messing around with search engine optimisation (SEO) tools without a good understanding of what they're doing.
Having said that, it can be hard to find (which of these thousands of Google requests per minute is causing the issue).
And the annoying thing is that the culprit almost always knows they were causing the issue in spite of the any communication...
Biting the hand that feeds IT
