Mike Malloch argues that groupwise tagging for semantic content is a key research problem, because it does not work well currently, and for social software that is the primary way in which the program can learn about the user/learner's understanding.
S. Hausmann, und K. Götzelt. Tagungsband der Multikonferenz Wirtschaftsinformatik (MKWI), Seite 1461--1472. Göttingen, Universitätsverlag Göttingen, (Februar 2010)