I agree about The Fast Diet (but don't buy the recipe book by accident like my sister in law did). I'm currently reading my fourth book on the subject since the middle of April!! Obsessive or what? I'd say The Fast Diet was easily the best and the clearest. Luckily it was the first one I read.
Scunner, stick to your 600 calories on your fast days and you can't go far wrong. Some people say it doesn't matter what you eat on the other days and others say just don't go overboard and you'll be OK. I'd suggest that the 2nd bit of advice is nearer the mark. It's a fab diet but it isn't magic. You have to have an overall deficit in calories for it to work properly. If you're only eating 600 for 2 days a week you'd have to really overeat the other days not to lose weight though. Mind you, we had an Indian take away last weekend, friends round last night for a barbecue and a Chinese just now and I'm still confident of a loss of some kind when I weigh myself on Tuesday so it is almost magic.
You do lose some of your ability/desire to stuff yourself silly too so that helps.
If anyone's thinking of starting this diet give yourself a week or two to get used to it and start noticing the benefits. The first fast day or three can feel really weird but you get used to it and it's really worth it. I don't feel like I'm on a diet nearly all the time and when I'm doing a fast day now I feel really great, if a little hungry. It's worth reading the book if you can bring yourself to do it too. Or just read stuff on the internet about it. The benefits are so much more than just losing weight.