Yahoo! published an update about its Yahoo! Application Platform (YAP) program, Yahoo! says "We currently don't share specific or overall numbers for YAP Apps. However, every developer receives data on how his or her app is performing, including installation numbers and active users.
Yahoo! and Zynga, are building features to benefit all types of YAP apps. Features include: Enabling more viral distribution of activity from apps via app notifications; Enabling users to share app Updates to social networks that drive usage back to YAP apps; Richer information to display in Updates; Creating channels to reengage existing users with installed apps; Additional canvases around Yahoo! where users can interact with apps; Continued support of OpenSocial and new versions that become available as standards.
And, that "we aren't planning on a paid distribution model. Developers are free to work with their choice of monetization provider with restriction that 3rd-party ad networks require Yahoo! approval."