1. A method implemented by a processor of a profiling system, the method comprising: based on a document corpus containing a plurality of documents, creating a topic set, at least some of the topics in the topic set being organized in a hierarchical structure which includes a plurality of topic levels including an upper topic level and a lower topic level, each topic in the lower topic level being a subtopic of at least one of the topics in the upper topic level; monitoring interest in a plurality of documents for a user to identify one or more documents-of-interest to the user; and based on the monitored interest for the user, creating an interest profile for the user by: determining a measure of topical interest for the user for at least one of the topics at the upper topic level and for a subtopic of that topic, the subtopic being at the lower topic level; and determining, by the processor, a per-topic heuristic feature profile for the user, the per-topic heuristic feature profile indicating non-content related features which affect a user's interest in a document by specifying, for at least one topic of the topic set, an effect of document type on the user's interest in documents associated with the at least one topic, wherein the document type is one or more of: a blog post, a micro-blog post, a comment, or a news article.