I looked at this a couple weeks ago. The numbers depend on how you measure 'user' and 'location'.
Silicon Valley: 5% - 14%;
US: 32% - 56% (including SV);
Europe: 28% - 35%;
Canada/Australia/New Zealand: 7% - 8%;
India: 2% - 7%;
China: 0.5% - 3% (including Hong Kong). From European countries, the UK is 5-8% (of the HN total), Germany is 4-7%, France is 1-3%. The Dutch and Swiss are (stereotypically) stable at 2% and 1% respectively.
These ranges include measures like logged-in-ness. If you only look at total users then SV is less than 10%, and the US comes out less than 45%—or even as low as a third, depending on what's specifically measured.
Canada/Australia/New Zealand: 7% - 8%
Is this combined for all three, or each individually? If combined, could you break it down? If individually, wow for New Zealand!
Combined. I don't seem to have kept that breakdown, but it was about what you'd expect from population.