However, my instinct tells me that the example you mention of say, an ad + landing page, IS an MVP in one good sense - to gauge interest in a potential product (an iPhone app, etc), gathering subscribers to mailing lists, beta signups, etc.

But in the scope of what Diaspora is trying to accomplish, releasing the code base like this doesn't qualify as a product - I think.

I am way more than willing to be wrong on this point, though. I'm also probably just splitting hairs by this point.