The unfortunate thing about apps like these is that if you are wise enough to use it, you are wise enough to not need it. Totally anecdotal, but the people I know who have trouble managing money are just completely unaware of it. Money goes in and money goes out, and they only do something if someone calls them or sends them a letter. As soon as you show these people the numbers, they get it. It clicks for them. Mint…
You're totally right that people who have trouble managing money in general don't use these kind of apps. Before starting work on Penny, we asked a hundred or so people "how do you manage your money?" The prevailing answer was, "I don't." So when you give them the tools to do that, it really helps them understand their situation.
What we see as the real problem is comprehension and usability. Many people we talked to shy away from apps like Mint because they're complex and intimidating. From a more technical/analytical/affluent standpoint (where I come from), I don't have an issue using Mint and querying my own data, but it's important to remember that I'm different from most people. So, we think that giving people that awareness of their financial situation in a friendly, relatable, and understandable manner goes a long, long way.
Regarding continued use: everybody's finances are a representation of their life, and as life changes, your finances do too. So we think there's a lot Penny can do to help you on an ongoing basis, like tell you about how your new commute to your new work is affecting your gas spending and your savings rates; mention how Comcast just bumped your bill up by 10%; point out that your Starbucks spending has been trending up and might start being a significant money drain, etc. We might be wrong, but we think we and everybody else in this space have only scratched the surface of what insights can help people with their finances.