For starters from my past restricted perspective:
The global environment. USCs may not only have to worry about US/UK relationships if they've lived or worked elsewhere, but those of 3rd or 4th countries. Multiple tax treaties and 'source' of income become factors.
HTKO was mentioned in passing on one thread. It's become a hot topic for 2011. In prior years, handwriting on Form 1116 was involved, but this year it even has its own new, dedicated line for part of the declarations.
Tax code definitions, and the way the IRS accept filing differently from what seems logical by use of the code definition.
From recent posts I've noticed, these will effect some on UKY. From what I've read, only one of the above will be of concern to you.