From the Google Ajax Search Blog

<quote>
Our mistake was in taking a silent error and turning it into a noisy one, and I apologize for the painful process that many of you experienced. Your ability to react in real time to the changes helped us monitor and fix this in real-time, so we appreciate all the helpful feedback.
</quote>

Link:
http://googleajaxsearchapi.blogspot.com/2006/07/fix-for-key-validation-issue.html

I now added the Ajax blog to this page:
http://blogoscoped.com/google/