Situated dialogic corpora are invaluable resources for understanding the complex relationship between language, perception, and action as they are based on naturalistic dialogue situations in which the interactants are given shared goals to be accomplished in the real world. In such situations, verbal interactions are intertwined with actions, and shared goals can only be achieved via dynamic negotiation processes based on common ground constructed from discourse history as well as the interactants' knowledge about the status of actions. In this paper, we propose four major dimensions of collaborative tasks that affect the negotiation processes among interactants, and, hence, the structure of the dialogue. Based on a review of available dialogue corpora and annotation manuals, we show that existing annotation schemes so far do not adequately account for the complex dialogue processes in situated task-based scenarios. We illustrate the effects of specific features of a scenario using annotated samples of dialogue taken from the literature as well as our own corpora, and end with a brief discussion of the challenges ahead.