To date I've always used "All Languages" and "All Countries" for ad delivery. However, with my max cost now almost $1 for certain keywords I feel I should discriminate where the ads appear. What do most people do who limit the countries; do they first of all select the lot and then manually remove those countries they don't want to see the ad? Or, do they manually select the countries they wish to show the ad to? Not a lot of difference I know but I currently have about 4/5 countries who click a lot and don't buy anything and am undecided as to whether to simply deselect them, or click those countries who buy from us (probably about 10). 85% on the list neither click nor buy .... but they might in the future.
Also, can (and does) Google identify everyone by country? Can they really differentiate between people from Equatorial Guinea and Burkino Faso and therefore show Adwords accordingly?