That depends on how secure your password is.
If your password is "abc123", you will almost certainly lose your bitcoins to theft eventually.
If your password is "b678VvQ&*o78bvn2cv67^%@Ip59X#4x35Z", then it is probably secure enough.
By the way, late reply I know, but XKCD has a great comic about password entropy which you can find
here. "Through 20 years of effort, we’ve successfully trained everyone to use passwords that are hard for humans to remember but easy for computers to guess."
I don't think there is a clear answer on this yet.
There has been some discussion about several of the "break-ins" involving accounts with poor password security (same password used on multiple sites, and/or weak passwords).
There has also been some discussion about the possibility of weakness in the smartphone app where the password was stored in cleartext.
I think I remember there being some discussion about the potential for users to have encountered malware that may have captured passwords as well.
I agree about there being no clear answer - each case of theft is different and I've heard many stories of people having their coins stolen, not just from blockchain.info. There are numerous means that attackers can use to access your wallet, and protecting yourself from each threat should be of the utmost concern to every bitcoin user. I detailed in a previous post the steps that blockchain.info users can take to protect themselves, but honestly, I have to wonder why you would use a currency that was basically designed to circumvent banks and then entrust your money to an entity which is basically just a different form of bank.
I get that it's convenient. I just mean that if something does go wrong, you were pretty much asking for it.