Off the top of my head, Australia, new zealand, Canada, uk & Germany are all shorter(# years) and far easier(difficulty of visas, crap you have to put up with) to naturalize/obtain citizenship.
The US is one of the least progressive western countries immigration-wise.
Agreed -- and 4 years isn't considered "that bad" by many of my immigrant friends. I have several who have been in the US nearly a decade and are still waiting.
