Very good advice, from Megan McArdle.
If you think that they really need the money, and that you're not just helping someone dig themselves even deeper into financial irresponsibility, then my advice is to just give them the money.
Give them the money? I can't possibly afford to do that!
Well, my friend, given the default rates of primary borrowers, that is what you're doing when you cosign--with the additional cost of origination fees, interest payments, late fees, collection fees, a black mark on your credit report, and probably, a destroyed relationship.