The system is fully programmable. For example, you can tell your dishwasher to send you a tweet or text when it's finished. Or you can turn off your home's lights from your iPhone. Or you can get a text message whenever your doorbell rings...
You get the idea.
Manufacturers can also add Imp card slots to their appliances. (If an appliance doesn't have the slot, you can buy one and install it.)
Each Imp card will cost $25, but no word yet on when you can buy it. Developers can get their hands on a development kit in late June to start writing apps.