Lendingclub also went through a quiet period, so there is obviously some real reason for it. If Prosper's lasts as long at Lendingclub's ( 6 months) then they will not survive (IMO).
It appears that in both cases (Prosper and Lendingclub) the companies were told that they were selling unregistered securities and decided to go out of business (or were forced to) until they got their securities registered. IMO, in both cases they used the concept of a "quiet period" as a smokescreen/excuse for not answering questions or interacting with their customers subsequent to the shutdown.
Quiet periods, as the term is generally employed, do not include suspension of business operations. Some other things that Prosper is doing, such as (getting back to the specific subject of this thread) poofing forums, make no sense to me relative to a company quiet period. Quiet periods, by definition, are intended to prevent premature disclosure of inside information. How could a customer forum do that, unless an insider posted there?