There are all kinds of difficult situations in the world that deserve the drive and intelligence that gets devoted to startups, including: HIV/AIDS, human rights (my background), global warming and the list goes on.
In the US, many of the most problematic and disruptive issues are economic (just ask all the people whose homes are going to be facing foreclosure over the next 2 years). Because of this, the startup I'm with has decided to do something to help consumers make sure they are on track for a secure and meaningful retirement (as one of the financial planners we're working with points out, you can't eat your house and retirement is the only thing you can't borrow for). There are all kinds of stories about retirements that have been derailed and we're working to make sure that everyone with less than $1 million will have access to unbiased, personalized and affordable advice.
PBS's Frontline did an excellent series that covered some of the unfortunate Americans who are struggling to make ends meet in retirement or saw their pension plans raided:
http://www.pbs.org/wgbh/pages/frontline/retirement/stories/
The stress that results in financial difficulty can be enormous and having enough money for retirement is the #1 concern for consumers in their 40s and 50s. What will happen if this issue doesn't get solved?
It's hard to say what measures will be successful, but I know that everyone involved with Boulevard R feels that if we can give consumers an online process to prepare for retirement, make the interface engaging, track their progress and deliver customized content then we are really providing a social service.
I love to talk about social ventures so feel free to get in touch. Here's a great company that's creating LEDs people in developing countries:
dlightdesign.com