I used it for a few months and it worked great. It gives you awesome perspective on how many calories are in things. I don't even need to use it anymore, just what I learned with a few months of using it has totally turned my lifestyle around. Now I just go around inwardly laughing/scoffing at the people that think they're being "healthy" and really aren't. A lot of people go to Subway because it's a "healthy" place but probably 95% of the things I see people order in there are worse for you than a Big Mac, with many of them being 2x as many calories or more for something that "seems" healthy.
It also gives you some good insight on stuff that can satisfy your cravings without destroying you. A Big Mac isn't *that* bad for you. It's when you combine it with fries and a 32oz soda or milkshake that things really get out of hand. To satisfy my burger cravings every couple of weeks I'll grab a bag of baked lays and grab a Big Mac with it for lunch. ~800 calories for a "cheat" meal that puts that greasy burger urge back at bay is a great deal.
The iPhone version of the app also gives you a pretty cool graph that really helps (my wife has an Android phone and couldn't find that option on the Android version of the app). It's really good because the graph turns red when you're failing your goal and that really calls out to your competitive spirit to get your #### in check and get that graph green again.
On your first pt, I am there right now. I can tell you how many calories are in 90% of foods without even looking them up now. I still use the site but often times I find myself only logging breakfast & lunch so I know how many calories I have left for dinnerOn your second point, this is so true. I try to eat around 600 calories for dinner. If one day Im craving pizza, I'll only eat 2 slice and thatll be 700 calories. As long as I dont eat a 3rd slice (which I used to do) or anything else for dinner its not even like a cheat meal.