Cairns I think you've hit the nail on the head when you talk about not worrying about gains. I think most dieting fails when people do get despondent about gains or stalls that they can't account for and the whole thing seems unachievable.
But, on the DD, after the first few weeks, I reckon every single person has realised that what you've eaten or how much you've moved about isn't immediately correlated with what the scales say. So then, the next thing that happens is, when you do get an "gain" day, instead of feeling cross or gloomy, it's easier to keep plodding on, on the grounds that one morning in the next week, 2k will suddenly have disappeared...taken away by the fairies...
That's my reasoning, anyway! Maintaining diet behaviour is totally psychological.
Today, I was down 0.6k, which makes 1.7k lost since last Friday. Who knows what the next week may bring? Bizarrely, I ate cold tandoori chicken and raita for breakfast, so will now look forward to my eggs with a nice salad nicoise for dinner 
PS Is anyone eating hot chocolate porridge? It is beyond divine...