You can listen to 1,000 songs per month for free without any special restrictions.
Yahoo! LAUNCHcast provides a free music listening experience supported by advertising. It's currently the only free service that incorporates customized stations along with unlimited artist, album, and song ratings. Unlike AM & FM radio, we pay royalties for every song and bandwidth fees for every minute of music that is played through our service. In order to have a free service for everyone, we have some restrictions on heavy use. These restrictions may be temporary and are subject to change as the dynamics of our business change. If your usage exceeds a certain number of song plays (currently 1,000 but subject to change) within a given month, you will be given the following option:
If you don't upgrade to Yahoo! LAUNCHcast Plus, you will not be able to use the service for the remainder of the calendar month. At the beginning of the next month, your free Yahoo! LAUNCHcast will be restored with an additional 1,000 songs.
Note: All songs played count toward the limit, including those that you skip.