Here is blog post which highlights why you should consider open source for your institution.
The information in the post mainly comes from public financial documents.
This recent discussion "Richard Stallman on Why schools should exclusively use free software" http://moodle.org/mod/forum/discuss.php?d=126957 is closely related.
I understand that my empoyer's agreements with Blackboard are coming to an end. The scuttlebut is that it is not going to be renewed. After reading that item Colin, I am not surprised..