Over the past decade, a lot of research has been done to develop efficient routing protocols for Delay- and Disruption Tolerant Networks (DTNs). In the course of this work, many comparative evaluation studies have been done to determine which of two proposed protocols is the better one (for a given situation). The majority of these evaluations are based on results gained from simulated network environments. In order to conduct a relevant evaluation of routing schemes, numerous conditions, policies and data need to be specified and fed into the simulation environment. The aim of our work in this paper is to discuss current DTN evaluation practices through a thorough and critical literature study. Based on the surveyed material, we show some weaknesses and lack of argumentation used in the evaluations. Through this, we hope to aid in bridging the gap between simulated and real-world DTN environments. In addition, and as a call for further research, we propose a model for evaluation of DTN routing schemes that outlines the most crucial inputs that needs to be considered in the evaluation process. This model is then projected onto evaluation practices used for evaluations of DTN routing protocols in a set of sixteen papers roughly covering a decade of DTN research.