There's a story on Ars Technica about smart appliances, which work with smart electricity meters to move your electricity demand to times when overall demand is lower.
It works fairly simply by detecting small changes in the frequency of the mains supply. These occur when the grid is working harder to deliver electricity. They're also likely to be the times when the most polluting generators are switched on to cope with the demand.
By switching off non-essential devices, the system smooths out peaks in demand. In fact, peaks can be reduced by up to 50%, which is huge because those peaks are the most expensive to supply. So, for example, the system might switch off your fridge and freezer for the ten minutes at the end of the world cup final when everyone is making tea.
There's a long term advantage to this system - it means that we can focus our future development on providing base load, rather than peak demand. Given that we're in process of introducing variable supply (with wind generators), it's a good time to be smoothing out the variable demand, at least somewhat.
I should comment on the fact that the article talks about electric water heaters. Of course, we know they're less efficient than gas heaters at the moment. However, given that you can't capture the CO2 from domestic heaters, electric heaters might become the greener option before long.
One of the schemes is described at http://www.thewattspot.com/. You're notified of price variations during the day, so you can choose to do your ironing, for example, at a cheaper time of day. The company sets hourly rates a day in advance.