1. A method in a server system for aggregating presence across multiple endpoints of a publisher, the method comprising: providing a collection of presence state publications for the publisher, each presence state publication having an availability value and an activity, the presence state publications including a user state publication and other state publications, the user state publication representing availability of the publisher as manually specified by the publisher and the other state publications representing availability of the publisher as derived from monitoring events indicating use of endpoints of the publisher, each presence state publication having a publication time; receiving at the server system from each of the multiple endpoints an indication of a presence state publication of the publisher; and upon detecting a change in the publisher's state by the server system, identifying a user state publication with the latest publication time; identifying other state publications such that user state publications with a publication time that is earlier than the publication time of the identified user state publication are eliminated from being identified; identifying from the availability value of the identified user state publication and the identified other state publications a least available state; and generating an aggregated state of the publisher indicating overall availability of the publisher from the collection of presence state publications based on the identified least available state so that the aggregated state is derived from the identified user state publication and the identified other state publications but not from other state publications with a publication time that is earlier than the publication time of the identified user state publication; and publishing the aggregated state of the publisher.