Nancy White on Sharepoint
If you don't know her, Nancy White is one of the leaders in the online facilitation space (she started and still moderates the onlinefacilitation yahoogroup, and she teaches an excellent and very intensive course in online work) as well as a number of other fields. I've known her for about a decade, enjoyed working with her a number of times, and come to trust her judgment highly.
She recently posted Tom Vander Wall Nails My Sharepoint Experience, which claims "SharePoint is a silo builder, not buster." I've never even seen Sharepoint, but I do sense that her words are worth considering when you're considering a tool to foster community.
Check out other parts of her blog, too; you might find you like it.
Incidentally, David Woolley's Thinkofit Web Conferencing Review has long been a classic place to see what online tools exist.