Taking into account population size, are these the 5 best visitors to have for your website?
 

After I've added population size into the calculation, these are the surfers who were most likely to buy (according to my stats). Overall I make most from USA (like almost all of you), UK is second, but per surfer they rank in the order below:-

1. USA
2. Australia
3. Canada
4. Sweden
5. UK

How does this compare to your stats?

Interesting metric, but how is population size relevant?

For example, I get my 2nd most sales from UK, but if I get an Aussie to my sites he's more likely to buy than a Brit

Yep but I still don't understand why population matters, rather than just concentrating on $ per surfer from country X?

You're right, doesn't matter much from our perspective, but I was curious to see how well countries were performing given their population, ultimately like you say $ per surfer is more important, I wasn't sure if US would still finish top per head of population, but it did