I'm happy to report that we've just committed code to our Subversion repository that implements searching. It should be noted this isn't just your run of the mill search support. We're looking to use the search feature as the basis for all content syndication and with a little planning this, too is working!
The trick is we defined very generic models for both the search response (denoting a collection of results) and the search result. By having this generic model, we are able to very quickly switch between HTML, RSS and ATOM (thanks in part to our liberal use of Zend_Feed). What to try it out?
First go to the Search Page or use the now functional search bar in the header of each page. By default the system will return the HTML results, however, you can quickly convert this to atom or rss by adding those terms to the search string. Here's a clear example:
HTML output: http://www.aptitudecms.org/system/search/?q=Releases
RSS output: http://www.aptitudecms.org/system/search/?q=Releases&rss
Atom output: http://www.aptitudecms.org/system/search/?q=Releases&atom
One other note is that each search you do that has results will give you the familiar RSS icon in the address bar of the browser (at least for the browsers I tested). I see us using this feature to make it easy to embed new feeds in the plugins and even extend this so that you can customize the name, etc of the feed for anybody that might consume it. Additionally, we'll likely add additional output formats (e.g. AMF).