Thanks for chiming in, I share your view. I too still have my concerns despite all the security measures taken. If it's not 100% and someone else has the keys it's compromisable. I'm not bashing your service at all, just having that splinter of doubt...
There's a tough balance to be struck between security and convenience. When it comes to cryptocoins, the most secure option is for everyone to have their own PC wallets (or Trezor) protected by an unbreakable private key and behind a superb firewall. I heard of one person who kept a wallet like that and only took down the firewall once a week to check his balance. Even better, each individual wallet holder would take the time and effort to learn how to make a paper wallet and keep funds in cold storage. He or she would know how to encrypt flash drives and keep the wallets there so no one could ever touch them. He'd also know to keep those duplicated and stored in multiple locations that only he knows about. And it goes on...
The reality is that very few people are going to take these measures because while secure, they are inconvenient. When it comes to everyday use, we'd rather go with "good enough" in terms of security in favor of ease of use and convenience. DNotes' goal is for mass adoption of its currency, mainly, to be adopted by people who do not have any experience with Bitcoin to date. These people will use DNotes if they see a benefit to it, but they are not going to take the time to figure out PC wallets, paper wallets, encrypted wallets, or anything like that. Those things are entry barriers. Even without dealing with a private key, I personally gave up on my PC Bitcoin wallet months ago because it takes so darned long to update the block chain--it's too much of a burden on me (not to mention my patience) as well as my computer's resources. The reason I can keep going with Bitcoin is thanks to online wallets like Coinbase and trade exchange built in wallets. Yes, I'm trusting a third party to keep my funds safe, but it's easier than dealing with the entire block chain.
The DNotes team understands this and has come up with a system which is very good from a security perspective, but also very easy and convenient to use. This lowers the adoption barrier as anyone with some Internet experience can find their way around a DNotes Vault account. There's a much smaller pool of people who are willing to deal with all the hassle of downloading and encrypting QT wallets and also keeping up with their updates.
It does make sense for any cryptocoin at this point to cater to both types of adopters. However, if you can't please everyone, the reality is your larger pool of potential users comes from the folks who want convenience and ease of use and are fine with "good enough" in terms of security. It's that larger pool that DNotes is after.