I am a big fan of loyalty schemes in general, as long as you are a savvy shopper and realise their true worth and not get 'sucked in' with buying things that you wouldn't normally buy or overspending, as other GNetters have said. I have a Tesco credit card but I loathe Tesco and hate shopping there, so I shop in Sanisburys, which I love, use my Nectar card, and pay with my Tesco credit card and so get two lots of reward points...lovely! However, I have had huge issues with Tesco when I was one of a supposed very small minority who's accounts were hacked and our points stolen by someone unknown. Their handling of it was awful.
I'm not sure a loyalty scheme would make me look at an energy tariff any differently - savvy shopping says if it's worth doing, I would do it, but just on rewards alone, I wouldn't choose a certain tariff. I'm not with Eon, and I would only move to them if the rewards made it worth me switching. I would like to add to my Clubcard point stash, as these have come in extremely useful for us as a whole family, treating the children and grandchildren to days out etc, but I don't want to have to pay through the nose in the long run for these rewards.