If I put Bitcoins into my blockchain.info wallet. Then I backup that wallet into Dropbox. Can someone still steal my Bitcoins?
Possibly. It depends on several conditions. Do you have a strong password on the wallet? Can someone access your Dropbox? Are you using 2-factor authorization on the blockchain.info wallet? Can someone access your 2nd-factor device? Do you use public computers to access your blockchain.info wallet? Do you have any virus, trojan, or other malware running on your computer when you access your blockchain.info wallet?
I'm trying to understand why I should transfer my Bitcoins from Coinbase into Blockchain. Blockchain.info kind of scares me because if for some reason I loose my password, I loose my Bitcoins.
With Coinbase, you are trusting a company full of unknown people to all be reliable enough and trustworthy enough to honor their promise that the bitcoins that you give to them will be sent on your behalf wherever you want them to whenever you want them to. There are many people right now who trusted MtGox with the same promise. It is up to you to decide if you can continue to rely on others to honor such promises. You have to trust coinbase to honor their promise even if they are hacked, if any of their employees engage in fraud, and if a government agency sends them a court order to freeze accounts.
With blockchain (or MultiBit, or Electrum, or any other wallet), you are trusting yourself to maintain a proper backup schedule, to keep your systems clean of malware, to choose sufficient passwords, and to remember those passwords.
In the end, you have to decide who you trust more, yourself or them.
Until these third-party accounts demonstrate significant transparency, a regular schedule of financial and security audits, and supply insured deposits backed by a a well known and reliable global insurance underwriter, I trust myself more.
