Zimbabwe and UN - A Joke

I guess...I am writing this more as a self help than anything else.
Relevancy of UN was in question when US was going to launch an Iraq invasion. I took it as one of the excuses of US to go to war. But now looking at recent happenings around the world, like what happened in Burma after the floods, in Tibet after China's crackdown and more recently, in Zimbabwe, I can't help but think about this question once again. Especially in Zimbabwe, when people are dying of hunger, no country in the world seems to have the balls to do anything for those poor people. The so called African countries, which have some kind of leverage in this case, at least on paper, choose to do lip service only. How can civilized world stand in silence again? Even after Holocaust, we let this happen again and again in places like Cambodia, Darfur (Sudan), Afghanistan, and now Zimbabwe. I guess, in future, just like Holocaust, we will remember these times and pay our tributes to the dead. We are good and doing that rather than doing something meaningful!
Is UN blind? Cab diplomacy achieves anything meaningful in such cases, where a democratically elected dictator is bent on hanging on to power even if it means killing his own people?
And then people blame US for not doing anything? What a joke!