You know, that's always been a bit of an odd one for me.

Is there an immigrant group that doesn't start out gen 0 in the 'ethnic ghetto' (well, aside from my own, which foolishly jumped in with both feet, bless 'em) and then the 1st gens started to assimilate?

Unless, of course, you come in as a part of the dominant ethnic group, in which case it's not so much a case of assimilation as it is unpacking.