Saw a lot of people mention it so I went and put a few days into it. I'm sure I didn't get it exact but I think I learned a couple things.

1) How many extra carbs that tea, coffee, and artificial sweetners are adding to my day.

2) That I seem to be getting pretty close to the ideal of 70% calories from fat but that one day with a few alcoholic beverages can really skew that percentage so there is a downside besides delaying the fat burning, adding empty calories, and of course all the other bad stuff.

One of the ways to success in any diet program (even WW) is to track what you eat....everything that goes into your mouth. Some people, including myself, don't understand why they are not losing weight.....then they go to fitday and consiously track for a few days....then they know why the scale/measurements are not moving. I feel using fitday makes me accountable...to myself. I hope that makes sense.....
Fitday is a great tool....I broke down and bought the downloadable version and I think it is much easier to use than the online version.

I don't use FitDay on a regular basis - mainly because I start to become obsessed - but do find it's useful to use now and again to make sure that I'm on track with my eating