I love the Google AJAX APIs. It took me less than an hour to make an Ajax Wiki Search ( http://chir.ag/wiki/ ) using it last year and I use it all the time. The thing that's not clearly evident when using these examples is that it's not just replacing a one-time REST/XML call with JS but a real-time ajax query which means we can call it in some pretty nifty ways.
I've used the chart API in an internal app such that the user gets a real-time feel of the data as they change the parameters without having to hit "Submit" every three seconds. Also note, the motion api is derived from the Gapminder organization they acquired in 2007.
I've used the chart API in an internal app such that the user gets a real-time feel of the data as they change the parameters without having to hit "Submit" every three seconds. Also note, the motion api is derived from the Gapminder organization they acquired in 2007.