Google's latest toy shows that they are still in land-grab mode. Most everything they do is about getting more real estate on the web and the desktop. To further their presence on blogs, forums, and places where AdSense rules, they've released a version 0.1 Beta of a Javascript search widget.
Calling this contraption an API is generous. It's a bunch of Javascript routines that you can muck with. It will change. They'll put ads in it eventually.
To do anything with this API requires a basic understanding of Javascript - and it has a severe limitation because you have to generate a API Key for every single domain you'd like to put it on.
Furthermore, blogger complains if you try to embed the example code in an iframe. So I've had to host it at another machine and set the src of the iframe to that address. And for that I need another key - for the domain of the other machine... Not exactly easy to use.
In comparison, Yahoo's search APIs are much more complete and much more elegant and useful.
All-in-all - a very early look at something, at least they're not shy about putting out half-baked clams... which is a good sign.