Made a few implied points more explicit and changed "transaction" to "address" in a few occasions where it was more appropriate
for e.g.
"Users of bitcoin own keys which allow them to prove ownership of transactions in the bitcoin network, unlocking the value to spend it and transfer it to a new recipient. " to
"Users of bitcoin own keys which allow them to prove ownership of addresses in the bitcoin network. Unlocking these addresses, unlocks any value associated to it and grants the user the ability to spend and thus transfer value from it."
Do key holders really own transactions? when someone transfers bitcoin to a user's address, is that transaction really theirs rather than the spender's? Isn't it more appropriate to say that the bitcoins associated to their address is theirs.
"Unlocking value to spend it and transfer it to a new recipient"
here unlocking value implies the "value to spend" instead of "spend the value", also, isn't spend and transfer the same thing? and a user could transfer bitcoins to an old recipient instead of a new one.
You can buy bitcoin using Purse.IO.
However I do not think it's a good idea to add purse.io to ways you can buy bitcoin because there is a chance that at any moment Amazon can shut them down and then the comment will become obsolete.
I took the Coinbase description from their own about page. They are not an exchange, since you do not exchange bitcoin with other users, you buy and sell it directly with Coinbase. The big value they bring is making it easy to use bitcoin.
Identifying the potential pains that Bitcoin can solve, quantifying how big of an impact the innovation can really have. This should hopefully get the reader excited about the possible power their code can have, and encourage them even more to learn more about Bitcoin.
As I read through the history of Bitcoin section I kept asking when are you going to get to the part about Bitcoin. I think half of that section is really events leading up to Bitcoin, as well Bitcoin didn't have any history until it was invented.
myarbrough@oreilly.com