The Yahoo! Developer Network blog just published an article I wrote about Yahoo! BOSS. It discusses how to use the search filters and query attributes with the BOSS API.
I’ve used these methods on V3GGIE.com, a vegetarian search engine and will be launching a new niche search engine in the next few weeks.
It’s a wee bit slow right now due to a multitude of API requests to Yahoo! Boss, Yahoo! Pipes, Flickr, Amazon, and more. Look for some upcoming posts about the construction of the site. Hopefully I can even describe caching and threading. Once somebody teaches me :).