On a very high level: at WUW we did once an empirical study, which prooved that the most important influence factors on the effectiveness of IT-supported learning envirnmentsare CONTENT and USABILITY.
While improving usability is a straight forward task that just needs to be done at one point of time when a package has reached stability, improving the creation, management and delivery of learning content is still quite a research-centered activity.
Everything that eases the (collaborative) creation of content, for example, by taking advantage of Web 2.0 technology such as AJAX, would make DotLRN a killer app. At the same time the organisation of content should be based on sound instructional methods, where templates for different styles of teaching (e.g. disance learning, blended learning, compliance management) do exist.