There are about 6 million addresses which have at least one unspent output.
So, there are not more than 6M people who trust/use bitcoin? Not a big number
This is not necessarily true.
There are many people who choose to use a hosted wallet. As such, they don't have direct control over any addresses that have any bitcoins associated with them. Instead they have an account at a service, and the service stores most of the bitcoins consolidated into just a few addresses.
This means there could be significantly more than 6 million people using bitcoin.
On the other hand, many people control multiple addresses ( I currently have balances in about a dozen or so addresses). This means there could be significantly less than 6 million people using bitcoin.
As you can see, it is quite difficult to estimate how many people are currently in control of a bitcoin balance. I'd personally guess that it's somewhere between 500,000 and 24 million.