I was pretty excited to see MFP integration with GC finally realized earlier this week.
From where I sit (based on only one full day of data) it looks pretty promising. I think the clear concept here is that MFP is in charge of counting what you eat and GC is in charge of counting what you burn.
Some personal data from yesterday—
From Garmin Connect I/0 Widget:
2,464 Calories Consumed
747 Active calories (burned)
1,717 Net Calories
1,610 MFP Daily Calorie Consumption Goal
107 Calories over MFP Goal
From GC Total calories widget:
2,573 Total Calorie Expenditure
1,826 Garmin BMR
747 Active Calories
From MFP Web App:
2,464 Calories Consumed
2,280 Daily Goal (1,610 baseline goal + 670 in exercise that day)
1,900 Calories Burned From Normal Daily Activities
If I take the 2,573 Calories GC says I burned on Friday and subtract the 1,900 MFP says I should have burned through "normal daily activity" the difference of 673 calories is very very close to the 670 that was added to my MFP daily caloric consumption goal as an exercise allowance.
In short, I am cautiously optimistic that all of this is working as intended. I would love to get feedback from others.