There is an extensive literature on task modelling related to the design of computer systems. Task analysis and task modelling have been widely recognized as central components in human-centred approaches. The aim of this paper is to report on some results of a worldwide survey about actual practices of task descriptions languages (TDL) in SIGCHI community. Results suggest that academic TDL are not well known and not used by participants. They prefer using “home-made” TDL. This may be explained by the fact that formal TDL are not adapted to tasks analysts needs and that task modelling is an expert activity, mainly used by skilled analysts. Indeed, this study shows that task models are not only used in a productive way, i.e. to derive useful inputs to the design of man-machine systems. Thus, it seems that formal TDL failed to take this into account.