I was wondering about this too.
I am from the UK and have just enabled her, (although she still isn't answering personal questions like others are reporting) and she seems to me to be fun to play with for 10 minutes, then I start worrying about things I ma missing from having my phone's region and language set to US, not UK.
At the moment these are the settings that have been changed to enable her:
-Added US keyboard (additional to UK one)
-Country/region: US & Regional format (phone language region)
-Speech language: US
I am not sure how much impact these setting will have, under the setting my phone says that the time and date are still the same as UK, but currency is now $, not ?, and if that impacts the store too, (which I don't know cause its not working) I will definitely switch back.
So guys, do you know any impacts of switching to US?