For me, I think it's more of a question of the money we save before the ARM reset vs the amount that we have to pay down to get a reasonable rate. We can handle the reset, but don't want to have to put too much money in real estate/housing, as I think the price is going to be flat to down.
Let's say we save $600 a month for 5 years, that's 36k. Now if we have to pay down 300k to get a decent rate in 5 years (we can handle it), then it might worth it. As I can grow 300k faster that the mortgage rate (5.125%). However, if the rate won't change much for a year, then I can still still refinance to a 30-yr fixed rate in a year and save some money, but it's a bit risky