Aside from being used to centrally manage how much electricity you can use, the Infowars crowd asserts that there is a still more nefarious purpose behind these. They assert that the smart meter interfaces with the new generation of smart appliances, basically turning them into a swarm of information-gathering devices that transmit data over the electrical utility lines.
Far fetched? Who's to say anymore? Anything is plausible now. It's very possible to turn electrical mains into dual purpose wiring, functioning as an electrical supply line as well as a data network.
I would really like to see gas turbine generators become affordable. "The grid" is more than just a supply vulnerability, it's very literally Leviathan's tentacles.