WebmasterWorld's moderator, incrediBill, posted a thread at WebmasterWorld noting that Yahoo's URL Ping server seems to have gone offline recently. As he explains, when he tries to access the documented Ping URLs, he gets a dead response.
Try it yourself, try sending a ping via the documented example URLs:
The API URLs are dead as well, see http://api.my.yahoo.com/rss/ping?u=.
Is this the beginning of the end to Yahoo Search?
Forum discussion at WebmasterWorld.