Your credit and your wifes credit are 2 seperate things. The only time your credit is considered together is if you need to use both your incomes to obtain credit.
Usually this happens with a mortgage, where both peoples incomes are added together if you need it to qualify.
It can also happen in a situation where say a wife with good credit, obtains alot of credit, and owes more then 75%, based on the fact the husband who was not considered in the loans is helping her make the payments. When she goes to get credit, her debt service ratio, and credit utilization is too high and dispite her immaculate payment record and perfect credit history she'll be denided credit. Forcing the husbands credit to be taken into consideration in order to "count" his income.
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Ferrari F2007