You piqued my interest, Jeff, so I did check out ninjablocks.com. They have a cloud service (ninjablocks.com/cloud) that appears that the whole heroku/pusher bit might be unnecessary. The hardware is open, so you could build your own, or they are also doing limited runs were selling them for $155 AUD ($160 USD, £100 GBP) for the basic device, more with sensors and stuff.
I suppose one could also use IFTTT recipes too, again to get around the server bit. Still, this is more DIY with websockets, so that's got a big cool factor.
Yeah, building it yourself isn't the cheapest solution - but it is the most fun and interesting in my opinion. A Belkin WeMo (which integrates with IFTTT) costs $60 per outlet, so it ends up cheaper but again..less fun
I suppose one could also use IFTTT recipes too, again to get around the server bit. Still, this is more DIY with websockets, so that's got a big cool factor.