There already is a world government on some levels. The UN, WTO, WHO, etc.. are all global forms of government, their power is just limited.

I think the idea of a world gov't would be good, global cooperation is definitely better than global competition. I don't see why it needs to be any more or less good or bad than any of the national gov'ts around right now. That said, it's probably not something that's going to happen in the foreseeable future.