On the security side,they are pretty much dominant over the hackers since they don't have access to the private keys or URL identifiers.
Assuming a hacker somehow manages to get the Login Identifier,I'm pretty sure accessing the password is a tough nut to crack.Other way round,if the manager to hack the database for password hashes,getting the Login identifier is almost impossible.
So I'm still okay with using the service.
So do I, I haven't any issues with them for almost a year even though I am being worried about this problem but they already resolved it immediately. Since they are web wallets this is the risk that many are saying that we shouldn't use web wallets for storing our bitcoins. Still I will go with their service if something happens again for worst then I will pull out using them.
Main point of attention is that you don't use it to store all your coins there for a long time as there is a major risk as theoretically everything can be accessed online by an hacker.
If you just stick to using it with small amounts for your daily transactions since it's more convenient than a heavy desktop client, then continue using it.
Despite of their frequent site issues I find it an advantage of blockchain.info that they supply you with your private keys. If the site for example is offline, you'll still be able to access your coins.
I can't think of any way that a hacker can have your coins in block chain unless they will penetrate directly to BC's database. But accessing online with your account seems to be a hard thing, they need to find out first your private key before they can have access with it.
It of course doesn't mean that during the time that you make use of blockchain.info that such a thing will happen, but I always try to be one step ahead where I don't expose my coins to unneeded risks.