[erikbye]

Wherever you purchase some coins transfer them to your private wallet/cold storage. One thing is the need to own your keys and thereby your wallet, but you also should not trust that your exchange will keep your coins safe, or even that the exchange will be there tomorrow.

[chx]

This is the biggest hurdle to become mainstream: in the hustle to decentralize money, bitcoin hustlers have decentralized security and most people absolutely suck at (cyber)security. Previously perhaps you needed to reinstall Windows or even lost a few (or more than a few) documents but now you will lose this thing you paid for and the thief can easily turn into real money (and hard to track at that).