Anyone who thinks that Google Adword is delivering you ads to certain country, dream on. I just had interesting experience. Awhile ago I started campaign targeting only us visitors and while visiting sites from where my visitors are coming from I was actually able to see my ad and I'm not from US.
for me it worked perfectly that feauter.. i have targetted my campaign to ARgentina, and if i search any keyword in google spain, or google france, or any country except argentina, the advertising does not display