I'm in. I've looked at the numbers, and in my situation, paying the mortgage is the way to go.
I live in a mobile home, with 6.25% interest rate for 30 years. The House won't be worth anything in 30 years, its worth is steadily declining. We probably can't refinance it, either. Had a hard enough time getting any loan at all for it.
However, things are looking up since I started being Mustachian. I'm 5 years into it, and I've still got $72,000 left to pay on the principal... but $85K more just in interest if I keep going.
So, tax return (about $3900) is going on the mortgage, and I'm putting down an extra $500 a month. At this rate, we'll have it paid off (and not have paid an extra $85K) by 2020, if not sooner. Then we'll have $1200+ extra a month to invest.