This interesting opinion by Harold Meyerson in the Washington Post focuses about the negative impact of the abusive use of temps that are not really temps. The only remedy is to make all temps eligible for the same full time benefits as the 'regular' workforce: that's the law in most industrialized countries where you cannot hire 'temps' without providing them with full benefits, proportional to the duration of their work, ie if you worked one month you accrue 2 days of paid vacation, if you work two months 4 days, etc.
The companies that claim to be responsible corporate citizens should show the way by requiring that all the 'temps' they eventually use do obtain full benefits. For most of them this would only represent a very small share of their profits.
This system works in all the other industrialized world where those global companies profitably operate, why not in the US?
It is up to the people, the customers those companies depend upon to require that they do the right thing. The companies that will lead the way will reap plenty.