23. A non-transitory computer-readable medium having stored thereon computer-executable instructions that, in response to execution by a computing system, cause the computing system to: receive from a client system an annotation of a digital work by a first user; store the annotation in a memory in association with the digital work; require a second user desiring to access the annotation of the first user to perform a specified action before providing an authorization credential to the second user, wherein the specified action is contributing an annotation of a digital work; and upon receipt of the authorization credential from the second user desiring to access the annotation, provide the annotation to a client system for output to the second user, wherein the annotation is provided in context with regard to the digital work.
23. A non-transitory computer-readable medium having stored thereon computer-executable instructions that, in response to execution by a computing system, cause the computing system to: receive from a client system an annotation of a digital work by a first user; store the annotation in a memory in association with the digital work; require a second user desiring to access the annotation of the first user to perform a specified action before providing an authorization credential to the second user, wherein the specified action is contributing an annotation of a digital work; and upon receipt of the authorization credential from the second user desiring to access the annotation, provide the annotation to a client system for output to the second user, wherein the annotation is provided in context with regard to the digital work. 26. The computer-readable medium of claim 23 , further having stored thereon computer-executable instructions that direct the computing system to store the annotation in association with particular content in the digital work.