A mood state may be modeled using mood information for a content selection (e.g., a digitally-encoded song) and/or by using mood information determined by how a user is interacting with a media player. For example, a playlist engine on a host may determine that a particular song is associated with an uplifting mood, thus determining that a user who has selected that particular song currently is in an uplifting mood, and correspondingly may select additional songs and advertisements consistent with, or responsive to, the uplifting mood. Mood information also may be used to present a mood state of users (e.g., co-users) in a network for display in a graphical user interface (GUI). For example, a user's screen name appearing in an America Online (AOL) Instant Messenger's Buddy List may indicate a determined user's mood, such as “happy”, “sad”, “silly”, or “angry.”