Historical data may as well be misleading because the profile of a user is not "static", simply because there's a human being behind it (and sometimes even more

Historical data may as well be misleading because the profile of a user is not "static", simply because there's a human being behind it (and sometimes even more than one, but that's another story). His personal and professional environment, his wishes and necessities, the context of his life may change from one day to the other. The assumption that the past queries of a user will improve the results of his current queries is at least questionable (especially for former programmers that start selling reptiles...)