I have the same issue
I just got a 2012 Focus Hatchback (Titanium) and I have to say that I do love the car. However, I have had the shuddering problem that you mention but I dont seem to have it to the extent you describe. I was sitting in traffic the other day for about 30 minutes and every time I inched forward my car felt like it was going to stall. This is a real pain in the neck to me, and am considering bringing it back to the dealer to see if they can change the idle speed, but Im not sure if they can. Overall the car is awesome, but this shuddering thing is something that Im really not wanting to live with for the next 8 years (or so)!
If anyone has any success stories on getting this fixed, I would love to hear about it!