MFP is excellent at making you face up to what you are actually eating. At first it was a huge eye-opener for how many calories were in everyday things - like a slice of bread is 80-120 calories etc. The article mentions fruit juice too - that was a big one for me as well. I figured that since I was not eating loads of pizzas and burgers etc that my calorie intake was probably "normal" but boy was I wrong and MyFitnessPal really helped understand that. Likewise it was good for a reality check that the 20 minute run actually was only like 150-200 calories burnt, not 750.
That was good, but where it really helped though was in measuring stuff out, and to realise what a serving really was. The biggest culprit for me was breakfast cereals - 30 to 45g of cereal is not a bowl full - it is a fairly pathetic covering at the bottom of your bowl. For years I was probably having like 4 or 5 (... or more!) servings of cereal (i.e. a full bowl, like it looks on the packet or on TV adverts!) a day without realising.
I'd recommend people give it a try, if only for a couple of weeks to get a grip on what the calorific levels of some of your staples are, and what a serving actually looks like. It is eye opening.