Every now and then we are reminded how much we rely on Google.
Over the past couple of years, Google has done some experimentation with using AJAX search engine results pages. In doing so, such experiments have broken the keyword-tracking functionality of analytics tools because a full set of referrer data was not being sent (anything after the # in a URL is not part of the referrer string). Once Google were made aware of the issue, they rolled back and things went back to normal, where analytics packages could continue tracking referring keywords.
The visual change of the AJAX implementation was unnoticeable to an end-user, but the impact for Webmasters was immense. Earlier this week, it was noticed that Google was again not passing referrer strings. Matt Cutts of Google commented to let us know that the changes were an error on Google's part due to repurposing of old code. However, ever since the first implementation of the AJAX results pages, my Firefox installation on my Mac continues to show me AJAX results pages, not the regular ones. So, I have no doubt that there is still some Google traffic out there that is not sending referrers/keywords correctly.
It's just another reminder that if Google did want to make this change and not listen to us, they could really cause a big nightmare for all of us SEOs out there!