My goal is 30% or less in fat; I've been steady at around 27%, and steadily losing, too.
I thik the % are great to help you keep track; if your fat gets a little high just look back over the day at what you had, and tweak it the next day to try to get it down. the % also can tell you (sometimes) why you aren't losing...like your sodium content. Unfortunately it can't foretell TOM or other stuff that affects your weight.
I do fitday as a way to keep myself accountable, and so that if I do gain, I can look back and see where I slipped. I also use it to journal out my food, so I am more aware of my choices, and to make better choices. Prevents mindless eating, I find. Above all, it tells you your cals so you can make sure you are staying within the correct range to be successful.
Everybody is different, and what works for me may not work for you. It's a matter of knowing your body, and fitday is a great tool to get to know what will or will not work, because if you are in a losing streak, then all of a sudden you start gaining, you can look at the % and cals and perhaps see an area you might have missed for that day. What fitday does is give you an honest look at your eating habits, because sometimes we tend to overlook small areas that could make all the difference, but it takes you being honest on fitday for that to happen
so let's say you're at 40% carbs, 35% fat and 25% protein and you gain weight; try upping that protein through leaner choices like turkey or chicken breast instead of those nuts you ate yesterday, so you can up your protein and lower your fat at the same time, and flip flop the fat and protein % to 25% fat and 35% protein. For the record, I start to gain at 30% fat or above, so that is what I focus on; keeping that fat down and the protein high is what works pretty well for me.
Doing just that, I have lost weight continually for 4 weighins in a row after a week of plateauing. Hope this helps!