Here is a link to an interview with Vic Gundotra (a Google VP) where he discusses the load on App Engine as people started voting and posting questions for President Obama's Town Hall Meeting.
The video is less than 3 minutes long. At about the 1 minute mark, they show a graph of the load factor over time. It maxed at about 700 queries per second.
In the Google App Engine there are no code or config changes required as it scales to very large loads.
My definition of "Cloud Computing" is:
-- no code changes required for scaling
-- no minimum cost (zero use == zero cost)
-- no preset upper limit
To me, "Cloud Computing" means using computer power the same way as we use electricity. Use as much as you want when you want, and you only pay for the amount used.