Finally I put the code for the converter (Blackboard->Moodle) online: https://github.com/kraebsli/BlackboardMoodleConverter. It converts just the content, puts folders simply in sections. Complex Blackboard courses with deep folder structure may require a more intense postproduction.
Presentation on slide share: http://www.slideshare.net/brillux/converter-blackboardmoodle2752015
Presentation from iMoot2015 on Youtube:
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