10. A method comprising: by one or more computing devices, for a first user and a second user, determining that the first and second users share a common interest in a plurality of common-interest information topics based on an information profile of each user, wherein the information profile of each user comprises a plurality of information topics of interest to the user generated from a collection of information associated with the user, for each information topic of the plurality of information topics, determining an interest score, which indicates a level of interest the first user has in the information topic relative to other information topics within the plurality of information topics; and for each information topic of the plurality of information topics, determining a second interest score, which indicates a level of interest the second user has in the information topic relative to other information topics within the plurality of information topics; wherein the determining that the first and second user share a common interest in a plurality of common-interest information topics is further based on the difference between the first user's level of interest in an information topic and the second user's level of interest in an information topic, as determined by the interest score and the second interest score respectively, being less than a threshold difference; determining a common-interest strength between the first and second users, wherein the common-interest strength is calculated based on: a respective level of interest, as determined by the interest score and the second interest score, by each of the first user and the second user in the plurality of common-interest information topics, a number of common-interest information topics that are shared between the first and second users, and a correlation and a difference between the respective level of interest in the plurality of common-interest information topics by the first user and the second user, the common-interest strength measuring a connection between the first and second users; and establishing a connection in a social network between the first and second users based on the common-interest strength.
10. A method comprising: by one or more computing devices, for a first user and a second user, determining that the first and second users share a common interest in a plurality of common-interest information topics based on an information profile of each user, wherein the information profile of each user comprises a plurality of information topics of interest to the user generated from a collection of information associated with the user, for each information topic of the plurality of information topics, determining an interest score, which indicates a level of interest the first user has in the information topic relative to other information topics within the plurality of information topics; and for each information topic of the plurality of information topics, determining a second interest score, which indicates a level of interest the second user has in the information topic relative to other information topics within the plurality of information topics; wherein the determining that the first and second user share a common interest in a plurality of common-interest information topics is further based on the difference between the first user's level of interest in an information topic and the second user's level of interest in an information topic, as determined by the interest score and the second interest score respectively, being less than a threshold difference; determining a common-interest strength between the first and second users, wherein the common-interest strength is calculated based on: a respective level of interest, as determined by the interest score and the second interest score, by each of the first user and the second user in the plurality of common-interest information topics, a number of common-interest information topics that are shared between the first and second users, and a correlation and a difference between the respective level of interest in the plurality of common-interest information topics by the first user and the second user, the common-interest strength measuring a connection between the first and second users; and establishing a connection in a social network between the first and second users based on the common-interest strength. 13. The method of claim 10 , further comprising facilitating exchange and share of information items among the first user and the second user.