a united world is a nice idea, but it requires a lot of time. There is still a lot of conflict between people, not for economical resource only, someone still wants libery, other still want their religions to dominate.
I don't think the UE will reach most of the non-european countries. Some europeans still remember the problem that countries like Grece or Portugal had to enter the union.
It would be great, but i don't think i'll live to see it (i'm 18, so figure...)