Do they really mean unlimited queries? I think they need to do or say more to assure the developers they really meant unlimited.
The API can be found at http://developer.yahoo.com/search/boss/boss_guide/index.html and it seems very simple:
http://boss.yahooapis.com/ysearch/{vertical}/v1/{query}?appid=xyz[¶m1=val1¶m2=val2&etc]
vertical - web , image , news...
query - text query
appid - your Yahoo application id
parm1,2,3 - filter, type...
filter - -hate , -porn...
type - pdf , html , nonhtml , ppt ...