If you're a joint account holder or co-signer, you are responsible for the entire debt, says Barry Paperno, consumer affairs manager with myFICO.com.

Not only does the obligation go on your credit report, so does any bad behavior by the primary account holder. If you have co-signed for your husband's auto loan and he stops making payments, those delinquencies will go on your report, too.

Don't do it at all unless you can "afford to pick up the payments" if the other person stops paying, says Jill Gianola, CFP and author of "The Young Couple's Guide to Growing Rich Together."

Student loans are another sticky area where it pays to be especially careful.

Student loans are discharged (dissolved) at death unless there is a co-signer, says Gianola. Then, depending on the lender, the co-signer could be on the hook for the entire bill, she says. So, while spouses frequently co-sign for each other's student loans, it might not be the best idea for their credit.