I've been playing with a few of these devices and have backed many of the others.
What I find disconcerting is how much reliance there is on sending device events to the cloud, even though they could be processing the data locally (those that have hubs or decent on-board processors).
I don't necessarily want someone else seeing every single event datapoint inside my house. What makes a lot more sense is to process and store primary events inside the house, then send important events that need, say, push notifications to mobile devices out there. A Raspberry Pi or BeagleBoard with 32G of storage can be set up as a processing hub for < $50. I bet they could make an integrated one with BT, Z-Wave, or Zigbee for a little more than that and sell it for three times as much.
If they want to enable access to the event or content stream from the outside world there are methods to poke holes through the router. I understand that those who insist on putting these services on the cloud are also doing it so they can upsell subscription services downstream, but I think they're being short-sighted when it comes to user security and privacy.
@raminf great points. I think this is early days and we'll see a lot of experimentation down the road. One reason to put it all in the cloud might be because it's easier in the sense of one fewer updatable device to have to worry about (vs. just update the server and all users benefit at once). When you start to think about privacy or corporate use cases, then the demands on having some of it off-premise will be there. Or at least encrypted! I can't recall any of these guys talking about basic encryption.