Maybe I'm wrong but I feel like I'm the only person who didn't find MyFitnessPal very helpful. I usually eat home cooked meals with lots of different ingredients. While it's possible to enter every single ingredient and the amount used into MFP, it takes forever, and probably isn't very accurate especially since I never eat all of what I cook in one sitting (I'll make 2 or 3 portions at a time, so I then have to figure out what fraction of the total I ate and divide my amounts accordingly).
When I eat out, it's usually at local restaurants/shops that MyFitnessPal doesn't know. And even when it's a common food that I can find equivalent listings for, the same dish at different restaurants can have very different calorie contents. Is my local sandwich shop's chicken caesar wrap more equivalent to the wrap at Panera or the one at Quiznos? I have no way of knowing.
And, I did find a few listings in MFP that were completely inaccurate. For instance, the calorie count they gave for a Trader Joe's bagel was at least 100 calories higher than it should have been, according to the nutrition facts on the bagel package.
I did find MFP useful for cultivating general mindfulness about calories - it got me into the habit of checking the labels on things more often. But I didn't have any confidence in the actual totals it was giving me. I was just trying to maintain a healthy diet rather than cut significant calories, so I didn't have big margins to work with.
I ended up dropping it after a month or two.