(Red) is kind of BS
This new Bono thing is kind of a lot of crap because Converse (owned by Nike) and the Gap make their clothes in sweatshops. So while you might be slightly helping (even that isn't certain as none of us normal people know where exactly this money goes) people with AIDS in Africa, you're simultaneously hurting poor people in other third-world countries by supporting corporate wage-slavery.
Furthermore, when students at the University of Oregon, as well as some other colleges, were protesting Nike's labor practices, Phil Knight threatened to withdraw a $20,000,000 donation.
I guess the net gain/loss of people in the third world as a whole is basically nil if you assume you're helping some people as well as hurting others, but I have my doubts about how much this money actually helps. Most companies donate 50% of your money to wherever it is they send it, and that's out of a pretty enormous profit when you consider how little the clothing costs to manufacture—due to their labor practices.
So actually, it's best not to buy anything from Nike or The Gap (and most other chain clothing manufacturers). If you want to help starving African children, there's a good idea of a charity called Heifer International you could donate to. They give people cows and goats and whatnot so they can have some degree of self-sufficiency. And they don't make the cows in sweatshops.