It looks like the custom search engine has been launched -- you can easily create your own vertical search engine and volunteer to collaborate on others. The product is tightly integrated with Google Co-op, but unlike that service, it's easy to use and understand.
In fact, I created a search engine that digs through Google related content. It's called "Googling Google Search" and gives you a good idea what you can do with this service -- in less than 10 minutes.
For a nice overview of features, read Philipp's post at Google Blogoscoped.