Checking on this one...e-mail sent out to one of our teams that has done some Flex work on YAP. I'm not sure if they will have samples but I'll let you know if something does come up.

Jonathan LeBlanc
Senior Software Engineer
Yahoo! Developer Network

Please see this topic:

http://developer.yahoo.net/forum/index.php?showtopic=387

We've updated the SDK to make the authentication flow a bit easier, especially for desktop applications.