We're with EDF. We'd never get a smart meter.

1. They tie you in to the company that installed it, and you can't do comparisons to find a better deal unless the meter is changed.

2. Concerns about 'spying' and 'hacking'.

3. Concerns about harmful waves - people say they get migraines.

4. People also say they hum and make an odd noise.

5. No benefit at all. One would put the cooker on anyway, turn on a light etc. What's the alternative? Light a candle and a campfire?
Nobody is going to go round the house turning off stuff that is needed.

6. If you're so thick you need complicated technology to find out which appliances cost more to run, you're a fool.

Several of these points have been raised by posters above, but I thought I'd offer my own thoughts.