Thanks, lyonsroar. This is a very common complaint for the PowerShift transmission. Dual clutch transmissions in general is a new technology for a lot of people. "Shuddering" is a very broad term that can vary in severity from person to person. And we know from several examples throughout different manufacturers that this type of transmission tends to be a little harsh at slower speeds.
As another example (albeit a normal automatic), my car "shudders" violently if I put it into Reverse gear right after I turn the ignition. It has this feature where it warms up the catalytic converter by revving the engine during startup automatically. So when I throw it into reverse, the entire transmission literally shakes violently and makes a loud clunking sound like it's about to rip itself apart. I freaked the f' out when I first discovered this after buying my car, thinking something was wrong. Turns out it's a built-in feature for most Aisin transmissions. Someone was explaining to me that I'd typically have to wait a few seconds for the car to warm up a bit. Never had a problem since.
Lots of cars come with quirks like that. With the EPA cramming more and more restrictions into our cars, manufacturers are thinking up unique ways of handling those challenges with their own patented technologies. The dual clutch transmission is another example that comes with its own set of quirks. Although now it sounds like this case is probably not normal, since no new car is supposed to shake to the point of spilling coffee everywhere. Notchy feeling of gears shifting, yes... but not physical violent shuddering.
I apologize for sounding so harsh and blunt in my post. It wasn't meant as a personal attack. But like I said you have to realize that the term "shuddering" can be interpreted in a many number of ways. Maybe a quick video clip through a cellphone or digital camera could offer a little more insight into the problem. In any case the OP did the right thing and got the dealership involved ASAP. They have the tools and knowledge to know if it's really an issue. I was just going by the brief description that was posted and the previous complaints of the PowerShift transmission being harsh (typical in Fiestas).