The demo mashup does two things. 1) It gets a RSS feed from Yahoo's "Buzz" page for the current most poular topic keywords on Yahoo, and 2) make a REST request to Yahoo's image search for those very keywords.
My intention was to use true and clean generic cross-domain proxying all the way, so that a generic RSS client in javascript would first go through the cross-domain proxy, followed by a REST request to the Yahoo search service. However, I couldn't find any clean and easy-to-use js rss libraries, so I kind of fluked out by building a slim php proxy for just RSS (which doesn't handle heirarchical and/or complex RSS items at all) just to trim down the code a bit. YMMV.
I didn't mean to use Yahoo at all, really, but their API dox where a little easier to grok than Googles. Sorry Google :| .