One thing keeps popping up repeatedly at me in this thread. Seems most everybody ('cept Somebody nicePantalones) addresses the question from the angle of what can you do individually.
Of course, since this is a large and convoluted set of problems and the "bee theory" sets in most of the discussion winnows off into an exploration of guilt and lack of empowerment.
One question: How the fuckety fuck is it in any way possible for one person to effectively address even a local ill affecting more than 100 other people?
Gandhi said: "Live simply that others may simply live."
I try to evaluate my life regularly and eliminate things that are causing me unnecessary stress. I've been going through my closet every six months and donating unworn clothing (even if it fits, even if I paid a too much for it, even if I only wore it once) to a shelter for homeless families. My new philosophy on clothing is: have less, launder more. We just downsized our home and are getting rid of as much furniture and stuff as possible -- much of it going to the aforementioned shelter, which always needs furniture for their temporary housing program -- since keeping stuff "just in case" we find a way to use it in the future is depriving others who need it right now. I try to buy products that exploit people to the lowest possible degree (I just got a shipment of yarn hand-spun and -dyed exclusively by women in rural communities in Uruguay, distributed by a nonprofit which provides them with enough income to support their families) and to keep the impact of my family's existence on the environment to a minimum (cloth diapers, energy-consciousness, recycling all my glass, plastics, and cardboard). We have more than a few luxuries, of course -- the Wii, cell phones, I drive a minivan for pete's sake -- but we live happily without some things many people take for granted, like cable TV. I practice random acts of kindness -- feeding other people's parking meters, picking up litter, etc. Before we had Pearce, Pedro and I routinely gave rides to hitchhikers (never when alone, though -- just to be safe). We took a guy all the way from Cleveland to Galax, North Carolina during a road trip to visit my family one Christmas. Without our help, it might have taken him weeks to hitch back home, and it was damn cold. It didn't do much for the global economy, but I know that Buck will never forget the nice couple that gave him a ride and three squares one lonely December.
I could do more. I could buy more locally-produced fresh food at the farmer's market (and I used to, pre-kids). I could trade in my van for a hybrid vehicle (but I won't because I use every inch of that cargo space on grocery day). I could walk more and drive less. I could buy organic products more often. I could remember to bring my own bags to the grocery store more than once every six weeks. (Another thing I was better at pre-kids.) I could donate a lot more money to charity, especially if my consumerist past hadn't gotten me into so damn much debt.
But I try, and I do what I can when I can to live as simply as possible. It makes my life better, and it just might make other people's lives less difficult in some small way. You never know what kind of an impact your individual actions will have. I believe in the ripple effect. If everyone puts in a little effort in whatever ways they can, things might not improve, but at least they won't get much worse.
Or, you could look at it this way: If we solve all the world's problems, more will rise in their place. End world hunger, and we have suffocating overpopulation. Educate everyone and see global underemployment. Cure cancer and watch people die of AIDS, or Parkinson's, or renal failure, or heart disease. Or worse, make a cure so expensive that only the wealthy (hint: that's all of us) can afford to live. Best to make our short stint on Earth as painless as possible for the people closest to you, and leave everyone else alone to suffer in peace.
I prefer the Gandhi approach, though.