Problems with US xbox in uk
1)NTSC not PAL (dosnt matter if you are using HD)
2) Games from Uk will not work on US console (for the most part their are some exceptions)
3) Voltage US power pack is 110v UK one is 240v, plug the US one in over here and it goes pop and smells funny, I know i got them mixed up and put a UK power lead in my US xbox power pack and it was all over very quickly fortunatly i picked up a replacment second hand in the US and have a spare UK power pack for while in the UK
I have both but i spend all time traveling so i use my US one in the US mainly (and as a media extender in UK) and my UK one at home and on the move mostly (its currently in korea with me a 220v ansd NTSC country)
4th point i just thought of is they aint that cheap in the US anyway you can get better deals in the UK (same goes for apple kit as well)