I don't think that because a system leads to some abuses it means it is inherently flawed.
Each system has its pros and cons. Currently, most of the western economical systems are capitalism-based, with some dose of socialism (welfare, taxes, and so on). This leads to abuses (people who need welfare not having them, people not trying to work because the unemployment assistance is enough for them, and so on), but this also lead to less inegality between people (a system with no welfare at all would lead to a segregation between the rich who get richer and the poor who get poorer). For instance, the children of disabled people deserve a chance in life - something they can't have if their parents don't get some form of assistance.
As for the third world countries... well for one thing, we (at least Europe) are partially responsible of their current state. We invaded them, created countries with no regard of the current ethnical distribution, and left after completely upsetting their economical and technological system (both of wich happened to be some centuries behind at the time). Just this point some people (granted, that's mainly Europeans, again) have to keep in mind.
Now to answer Dan's question : yes, I think there should be a global sharing of wealth, maybe on a personal rather than national level. People would be taxed according to their income, without any exception allowed (so that the middle class wouldn't suffer most of the taxes), and the global wealth redistributed on a personal level again.
Of course, a limit of wealth is not acceptable for the same reasons pathsrider invoked.
And the numbers of wealth redistributed would be fixed by the government, based on the income of every people concerned. Of course, this redistribution would not lead to an equal amount of wealth for everyone either (this would correspond to setting a wealth limit); the idea would be to help the less wealthy to live a less miserable life, and to try to earn more money on their own.
As for a global democracy... yes, it has its flaws. Maybe there could be a democracy on the country level, then a "one country, one vote" on the international level. But in any case I think a world government would have to be a very complicated structure, much different from everything we have in our respective countries, if we want it to be efficient.