Interesting post here summarising Credit Suisse’s Global Wealth Report. Basically to be in the top 1% of the global wealthy, you need to have $712,000 USD in net assets. To be in the top 10%, you need to have over $82,000 in net assets.
One percent of 7 billion is 70 million. So basically there are 70 million people in the world with $712,000 USD or more in net assets.
[EDIT] Actually, having just read the report, the results are expressed in terms of the global population of adults, 4.5 billion in 2011.