People don't like to accept but email and email lists are still the fundamental ways people collaborate on important and personal matters. Even though Yahoo and Google groups are not being talked about much, it wouldn't hurt if someone innovate on top of those same old method of communication.

Ultimately, it doesn't matter if data (email) is pushed to the user or user is pushed to the date (website). What matters is the quality and integrity of the content and communication platform. If people feel comfortable using your service, if your service is easy enough for them to use, you win.