Wife and I always pay off a big thing usually and then use any left over to add to savings or smaller things to pay off.
Paid off wife's car in '07 with the refund. Paid off living room furniture loan another year. Now it just goes towards paying down our 1 car loan or savings account or the little bit that remains on the only credit card with a balance on it.
I'm hoping this year if we do get anything back that it'll be enough to finally pay off the last bit of the one credit card with a balance we have that we've been paying off for a few years now. We had consolidated all our debts into one 0% interest AmEx back in 2007/2008 time frame that at the time totaled something like $25k. Last I checked, we owe about $1,500 on it. So close compared to what we started off with. But it was a good move to consolidate all our debts to 0% interest. Has allowed us to make real progress on the debt over the last few years.
Once that card is gone and the car loan is paid off in hopefully a years time, we'll be debt free except for the mortgage.