13. A user interface comprising: a display device; a user interface of said display device having a plurality of user interface screens, at least some of said plurality of user interface screens containing user-selectable objects; and at least one advertisement displayed on a currently displayed one of said plurality of user interface screens, wherein said at least one advertisement is selected from a plurality of advertisements to display on said currently displayed user interface screen based on at least one of the following criteria: topical relevance, contextual relevance, path relevance and cognitive prominence, wherein said at least one criteria includes topical relevance and wherein said topical relevance is a measure of a relationship between one or more topics associated with each advertisement and one or more topics associated with said user-selectable objects on said respective user interface screen, and further wherein said topical relevance is calculated as: μ T ⁡ ( a , p ) = ∑ i = 0 n ⁢ ⁢ δ ⁡ ( a ⋂ t i ) δ ⁡ ( a ) + δ ⁡ ( t i ) where δ is the distance of a topic point from a root node.
13. A user interface comprising: a display device; a user interface of said display device having a plurality of user interface screens, at least some of said plurality of user interface screens containing user-selectable objects; and at least one advertisement displayed on a currently displayed one of said plurality of user interface screens, wherein said at least one advertisement is selected from a plurality of advertisements to display on said currently displayed user interface screen based on at least one of the following criteria: topical relevance, contextual relevance, path relevance and cognitive prominence, wherein said at least one criteria includes topical relevance and wherein said topical relevance is a measure of a relationship between one or more topics associated with each advertisement and one or more topics associated with said user-selectable objects on said respective user interface screen, and further wherein said topical relevance is calculated as: μ T ⁡ ( a , p ) = ∑ i = 0 n ⁢ ⁢ δ ⁡ ( a ⋂ t i ) δ ⁡ ( a ) + δ ⁡ ( t i ) where δ is the distance of a topic point from a root node. 14. The user interface of claim 13 , wherein said at least one criteria includes contextual relevance and wherein said contextual relevance is a measure of a relationship between a theme of the respective user interface screen and a theme associated with each advertisement.