I put together a search form with options for site-wide or web-wide searches. The site-wide search is just a little hack really, putting "site:www.thesession.org " in front of the query.
It wasn’t quite as much fun to play with Google’s APIs as it was with Amazon’s. That’s partly because it’s not really aimed at PHP developers but mostly because they don’t offer the chance to use XSL for transforming the XML that gets sent back. Thanks to a package of PHP classes called NuSOAP, I was able to accomplish everything I wanted but it would it have been nice to have an XSLT option.
All in all, it was fairly straighforward. I’m thinking about using the same sort of thing here at adactio.