If guest worker programs are the most feasible weakening of international apartheid in the immediate future, they should be pursued with gusto. To the extent they appear exploitive or corrosive, the problem is not with the guest worker program, but the underlying birth-based system of restrictions on movement and ability to work and live. Toward the abolition of international apartheid!
Addendum 20071227: The author of Guests in the Machine has two great posts on the subject the last two days. Please read The Migration Package Deal and The Myth of the Migrant.