A word of caution. These surveys use Likert-type measures (e.g. a 10-point scale where 1 means "strongly disagree" and 10 means "stromgly agree") which are not benchmarked. That is to say that just as US $5 and DM5 represent the same amount but different values, answering 5 on those Likert scales can mean very different things for different people and diffierent cultures.
For example, they report the following response patterns to the item "Gauging Global Satisfaction" - where numbers represent percentages of responses gauging satisfaction 7 or higher on the scale of 1 to 10.
Own
Life* Nation World United States 64 41 17 Canada 67 56 18 France 57 32 10 Great Britain 54 32 22 Italy 53 24 9 Germany 49 31 11
It can be argued that for gloomy Germans 7 means an exceptionally high level of satisfaction, while for blissfully cheerful US-ers 7 means less than "just fine" and that means "not good."
Another problem is sampling. For most developed countries the samples were relatively small (about 500) which produces a relatively large error marging (about +/- 4.4% or about 8.8 percentage points). This means that, using the example above, the difference between US and France in satisfaction with own life is 64-57=7 thus being within the margin of error.
But more serious problem is the sample composition. In most developing countries, sample contains disproportionally urban population (which their methodological note acknowledges) and, I may add, disproportionally middle class population (since they are easier to reach). I guess including the rural poor would change the reported figures quite considerably.
For these reasons, cross-national comaprisons of these scores can be misleading.
Wojtek