The higher the GDP per capita, % of researchers in population, and mortality rate are, the more likely a country's citizens are to be interested in BTC.
Here is the Google Trends map ("Bitcoin" - darker = more searches per person):
[2005] Here is GDP PPP per capita:
[2008] Mortality rate:
[
?] #Researchers/million (still some big outliers, like Japan - but that could be from bad GTrends data):
Google Trends is a crap starting point to try gauging interest by country, but I'm not aware of a better data set. Incidentally, I was surprised to learn Serbians and Russians smoke more regularly than drink water.
Other points of interest: there doesn't appear to be a strong correlation between Internet connectivity and Bitcoin interest. There may be a strong correlation between average age of first sexual intercourse and BTC interest (or it's just Scandinavia biasing). While GDP PPP matches up fairly well, income disparity isn't a factor.
(on a serious note, if someone has actually found indicators, I'm eager to see them!)
