dotLRN does have the concept of a community being active only between two dates.  After all a class runs for only one term. There is also the concept of archiving a class after its over. I haven't used either very much yet but they ought to be usefull for conferences etc.

I agree that the dotLRN framework will be very usefull for intranet functionality.  Personally I like the idea of creating a "dotWRK" distribution that configures in a sensible way for a company. Perhaps Jade's work will evolve into that.