Have you used Moodle, Blackboard, WebCT, or Sakai?

Do you use Moodle, Blackboard, WebCT or Sakai to collaborate with students, faculty, administrators or staff? Which application do you like most? I am taking a Moodle online class now and like it a lot. It is easy to learn. I have just started trying out Sakai, anyone wants to share experiences with Sakai?