1. A method comprising: detecting one or more bursts of activity associated with a given user by processing activity logs associated with the given user, the activity logs comprising information relating to one or more local resources of a computing device associated with the given user; mapping the bursts to tasks performed by the given user based at least in part on records in the activity logs; generating a user model for the given user based on the mapping of bursts to tasks; and providing personalized query processing to the given user based on the user model; wherein providing personalized query processing comprises: uploading a given one of a plurality of different versions of the user model to a given one of a plurality of service providers implementing search engines, the given version of the user model being selected based at least in part on one or more characteristics of the given service provider and one or more user classifications associated with the given user; receiving a query submitted by the given user; determining a current task of the given user; sending the query and the current task of the given user to the given service provider; receiving personalized query results from the given service provider based on the current task of the given user and the given version of the user model uploaded to the given service provider; and presenting the personalized query results to the given user; wherein the given version of the user model comprises a first version of the user model associated with a first set of services provided by the given service provider; wherein the first version of the user model is different than a second version of the user model uploaded to another one of the plurality of service providers; wherein the second version of the user model is associated with a second set of services provided by the other service provider; wherein the second set of services is different than the first set of services; and wherein the method is implemented by a processing device associated with the given user.