44. A computing system programmed to provide a marketplace for annotations of digital works, comprising: a computing subsystem that receives digital works from a plurality of sources; a computing subsystem that receives annotations of digital works from a plurality of authors; a computing subsystem that receives requests for annotations from a plurality of users and delivers annotations to requesting users; and a computing subsystem that facilitates receiving compensation from users for delivery of annotations and distributing compensation to authors of the delivered annotations, wherein the compensation distributed to an author is conditioned on an indication of satisfaction from the user to whom the annotation was delivered.
48. The computing system of claim 44 , wherein the compensation received from a user is included in compensation paid by the user to access a digital work.