Doesn't make much sense to me - just from a cost standpoint - unless they think they can get a better price from their European suppliers / manufacturing and it is a big enough savings to ship the assembled vehicles back here.
It doesn't bode well for quality - I've heard from a former Chrysler employee that they ran durability on the "new" Fiat 500, a Rover Mini and a Sebring. At the end of the durability testing (which the Mini and Sebring passed), the 500 was in bad shape - the doors were literally falling off.
When the word reached the Fiat executives, they basically said that the tests were "not representative of real world operation". Yetti may know more about this, but it looks like the Fiat 500 will bring back memories of motoring in old Fiats in the U.S. - or waiting for yours to be repaired.