The lesson I learned from the Mybitcoin scam was to never use another online wallet again. It doesn't matter how secure the wallet is, there is nothing preventing the owner from walking away with all your money. Remember, Bitcoin has absolutely no property rights. This is a huge downfall that will have to be addressed before widespread adoption can take place. Until then, secure your coins yourself. The client isn't that hard to use and now has encrypted wallets. And this forum is full of ways to securely back up wallets.
That's the wrong lesson to learn. The correct lesson is, "be careful." And another good lesson is, "don't store lots of money with someone you don't fully trust."
ewallets are fantastic for small amounts of bitcoins, but large piles of savings should be properly stored on your own backed up wallet.dat in multiple secure places.
It's important to remember that every place you store bitcoins has risk. Holding a wallet.dat has risk of user error/negligence, which can be worse than the risk of an ewallet provider running off with your money. And there are things preventing ewallet owners from stealing everyone's money, 1) long-term profit motive and 2) genuine good character (which is the majority of business owners).
