I have experienced a similar issue. It usually happens when i first start the car after its been parked for a while. When i back out of a parking spot, and then try to accelerate forwards, it delays, stutters/flutters, then when i try to give it more gas, it shoots forwards. After the car is driven for 5-10 min, the issue goes away. As long as the engine hasn't been sitting for a while it doesn't do this (for example if i run to the store and an there for an hour or so, it will back up normally and accelerate fine). its after the car has been sitting for multiple hours (5+).
I have an automatic, but it has the Select Shift option. Not sure if its the combination of these options thats causing the issue, or whether its like everyone has heard (new tranmission that was pushed out the door too quickly and still has some design issues that are not yet worked out). I have also heard that the 2012 Focus is 'drive by wire'...which sounds like throttle/acceleration is controlled by electronics and the computer. Perhaps the computer is not functioning correctly or maybe a software glitch?
I owned a 2002 Focus ZTS before this, and that car did not have this issue. Probably because it was a pretty standard car, and didn't come with all the new electronics, etc. that this one does.
The funny thing is, i don't remember it doing this when i test drove the (2012 Focus) car...