I don't dismiss Moodle, Bill, I have just found the structure to be focused on the course. A prime differentiator of Elgg is that it centres on the person. A course is just a node in Elgg and not a space that you have to enter. Some comments about Moodle (2008) are here:

http://jarche.com/2008/01/review-moodle-teaching-techniques/

I would define "course" as something constrained by content/curriculum.

Most of my practice is in workplace learning. I find the course too constraining and find that performance support tools, expertise locators, communities of practice and collaborative applications more appropriate for learning at work.