There is an informative article HERE about the recent Wisconsin court decision regarding the unconstitutionality of the minister's housing allowance. As of now it only applies to Wisconsin, but apparently would also apply to Indiana and Illinois if it is not overturned. It could also potentially apply everywhere (though it doesn't sound like it will).
We have used this to varying degrees over the years. While living in a parsonage it didn't really do us much good (or we didn't use it to our advantage very well). It has helped a little more since we have bought a house, but we still did not abuse it like many pastors I know. I've always been a little torn. I understand the intent of it, but have never liked how some pastors abuse it and take their whole salary as a housing allowance.
At any rate, it will only apply to me this year and part of next year anyway. This article explains the situation pretty good.