When I signed up for this class, I knew what to expect, up to a certain point, because I had already taken a hybrid class a couple of years ago that relied heavily on Prometheus (the system that was in place before Blackboard). The one concern was that I wasn't sure how the whole assignment creation, submission, grading aspect would work. My hybrid class was big on actual deliverables, and did not place much emphasis on the discussion aspect - it was either 5% or 10% of the grade.
I think that collaboration is a cornerstone of learning, both in f2f environments and in online classes. Without collaboration students are missing out on an aspect of learning that enables them to better connect what they are learning with what they already know, and it enables new knowledge creation through the sharing of information. In a regular f2f class there may be a group of classmates that regularly meet and discuss things about the class, but most classes tend to 'clump' people together into loosely bounded clicks of people.
I think that the online experience unbinds those clicks and allows more people to join into the discussion and exchange knowledge and information. I've learned a lot from my classmates (both here and in 640). What I've learned are things that are either completely new, or different ways of approaching (or viewing) a problem. I've often gotten inspired by what others have posted, and it helps me improve as a student.
I think that there is a sense of community in online classes, and I saw that when I logged in the first time and saw people greeting each other with 'good to see you again'. I think that I don't get the sense of community right away, but by the end of the semester, as we've all gone through the course and as we see other people's knowledge, personality and background, that community is implicitly created and augmented as more students join different classes as the semesters progress.
I think that the threat to the community exists, but only if the instructors permit them to exist. There may be a provocateur in the group - a fire starter if you will; or someone who purposefully trolls around. These individuals may want to play devil's advocate, but if they consistently don't phrase things properly it can compromise the community. In this instance the instructor needs to pull these individuals aside and see what's going on.
Other threats may be the technological hurdles to the class. As a member of the iGeneration, I am comfortable with these tools and I don't generally see this as a threat, but there are others out there that are not as familiar with the tools and this may impede them from benefiting and contributing to the learner community.