Is it worth buying traffic other than US?
 

What countries traffic is really worth buying apart from US?

Canada? UK? Australia?

Are the ratios from these countries dramatically different than the US?

As a canadian webmaster, I'd say Canada worth a try!

UK is by far the best there is, the average spend is much higher that US, thats why its the most expensive

It depends what you want to do with that traffic.

If you want to convert it then it would depend on what kind of sites you're trying to convert.

If you're trying to build traffic trades then you might find that some surfers, like Russian, Japanese etc. are generally more productive .. although you might run the risk of your trade partners not returning so much because for some reason non-US traffic is considered to be of lesser quality.