For a very good look at life in these cities for workers see Last Train Home, a superb, emotionally-tense documentary following a Chinese family from a farming community as they move to the city for work in a clothing factory (without making any statement about conditions). I found it a really accessible and poignant film to understand a little better the Chinese drive towards personal independence.
Guangzhou is also in southern China and noted as a 'city of new wealth', just a guess on my part if factory life and migration is the same (I have no insight on this whatsoever).
http://en.wikipedia.org/wiki/Last_Train_Home_(film)