13. A non-transitory computer-readable storage device having computer-executable instructions stored thereon such that when the storage device is accessed by a computing device, the instructions are executable by the computing device to perform actions, comprising: identifying, for a given action, a trusted group of user accounts from a plurality of user accounts using a respective trustworthiness score for the given action assigned to each user account of the plurality, wherein the given action refers to an online activity that is performed by one or more users associated with respective user accounts, each user account's trustworthiness score being determined using inputs received from the each user account for the given action, the trustworthiness score being used to identify the trusted group of user accounts whose input is to be used to classify an item, wherein the item refers to an article of the internet that can have an action performed on it, and to identify other user accounts whose input is to be excluded from classifying the item the identifying comprising generating an initial trustworthiness score for a user account of the plurality using a trained trustworthiness classifier and a feature set about the user account, the trained trustworthiness classifier comprising a number of machine-implemented algorithms used to evolve behaviors based on input data, the feature set comprising online user behavioral features and static profile features about the user account, wherein the online user behavioral features comprise online activity features and the static profile features comprise user registration features the initial trustworthiness score for the user account is used at least initially to determine whether or not to include the user account in the trusted group of user accounts for the given action; monitoring inputs for the given action and about an item, the inputs about the item from the one or more trusted groups for the given action are used to classify the item as one of spam and non-spam, such that any input about the item from other than the trusted group of user accounts formed for the given action is excluded from being used to classify the item; and evolving the trusted group based on modified trustworthiness scores of the plurality of user accounts for the given action, each modified trustworthiness score is determined, in part, by a comparison of an input about the item from a corresponding user account and inputs about the item from other user accounts in the plurality of user accounts, wherein evolving the trusted group further comprises at least one of moving at least one user account into the trusted group that previously was not in the trusted group and moving at least one user account out of the trusted group that was previously in the trusted group.
14. The non-transitory computer-readable storage device of claim 13 , wherein the online activity features of the online user behavioral features comprising at least one of online browsing activity, electronic mail transactions and address book entries, and the user registration features of the static profile features comprising at least one of user preferences, age, gender and occupation.