13. In a computing environment including a behavioral targeting environment, a system comprising, a URL or URL pattern suggestion mechanism or both a URL and URL pattern suggestion mechanism, that inputs a set of users' visit logs corresponding to a set of users, and outputs suggested URLs or URL patterns, or both URL and URL patterns, from a set of users and a set of URLs visited by the set of users, each URL comprising a resource path with levels separated by a same path separation character, including by a process comprising: for each URL in the set of URLs, for a given URL separating out the levels of the given URL into a data structure comprised of nodes representing the respective levels of the given URL, and adding the data structure to a tree data structure, where the tree data structure is comprised of nodes that represent levels of the URLs and node-paths in the tree data structure correspond to the resource paths of the URLs, for each node of a plurality of nodes in the tree data structure, for a given node, calculating a first set of users comprised of users in the set of users who have visited the URL corresponding to the given node and calculating a second set of users comprised of users in the set of users who have visited a URL on a sub-tree of the tree data structure whose root node is the given node, given an input set of users, for each node in the plurality of nodes in the tree data structure, for a given node, calculating a first user set intersection comprising an intersection between the input set of users and the first set of users calculated for the given node and a second intersection comprising an intersection of the input set of users and the second set of users calculated for the given node; calculating URL similarity or URL pattern similarity, or both URL similarity and URL pattern similarity based on the first user set intersections and the second user set intersections; and outputting the URL similarity or the URL pattern similarity in decreasing order of similarity, or outputting both the URL similarity and the URL pattern similarity each in decreasing order of similarity.
13. In a computing environment including a behavioral targeting environment, a system comprising, a URL or URL pattern suggestion mechanism or both a URL and URL pattern suggestion mechanism, that inputs a set of users' visit logs corresponding to a set of users, and outputs suggested URLs or URL patterns, or both URL and URL patterns, from a set of users and a set of URLs visited by the set of users, each URL comprising a resource path with levels separated by a same path separation character, including by a process comprising: for each URL in the set of URLs, for a given URL separating out the levels of the given URL into a data structure comprised of nodes representing the respective levels of the given URL, and adding the data structure to a tree data structure, where the tree data structure is comprised of nodes that represent levels of the URLs and node-paths in the tree data structure correspond to the resource paths of the URLs, for each node of a plurality of nodes in the tree data structure, for a given node, calculating a first set of users comprised of users in the set of users who have visited the URL corresponding to the given node and calculating a second set of users comprised of users in the set of users who have visited a URL on a sub-tree of the tree data structure whose root node is the given node, given an input set of users, for each node in the plurality of nodes in the tree data structure, for a given node, calculating a first user set intersection comprising an intersection between the input set of users and the first set of users calculated for the given node and a second intersection comprising an intersection of the input set of users and the second set of users calculated for the given node; calculating URL similarity or URL pattern similarity, or both URL similarity and URL pattern similarity based on the first user set intersections and the second user set intersections; and outputting the URL similarity or the URL pattern similarity in decreasing order of similarity, or outputting both the URL similarity and the URL pattern similarity each in decreasing order of similarity. 16. The system of claim 13 further comprising a domain suggestion mechanism that suggests domains from a set of users and domains visited by the set of users.