For a while, Jen and I have mused over refinancing to a 15-year mortgage. The monthly payments would certainly be noticeably more, but we'd be done so much sooner, and we've been paying the mortgage down faster than required anyway.
It makes an excellent point, one I hadn't realized. If the difference in interest is small (as you can expect it to be), keeping a 30-year mortgage and paying it off on a 15-year schedule has a total price tag not much different from switching to a 15-year mortgage. The difference is small enough that I think it's a worthwhile price tag for the luxury of not being locked into the higher payments.
And, it saves us the work of pricing mortgages. Win-win!