Linked here is an interesting article regarding the "second coming" of community web sites. Along with the author, I remember the first attempts (anyone else have a geocities.com site?)
Content (blogs, IM, pictures, music) and increased functionality (instant downloads, integration with other familiar applications) appear to have made a big difference from the first attempts at creating online communities. Likely the same holds true for online learning communities. The more learners feel comfortable and connected to the "community", the more they will be attracted to the online learning experience.