So I bought 2 mountain bike tires too, and hung all the new tires on the wall in the garage. (good place for them, right?). Well, today I went out to the garage and something drew my eye to my mountain bike's rear tire. I was appalled when I saw what it was--see it in the photo for yourself! (tube bulging out through hole in tire). I rode that bike 22 miles with relatives for the Metro Grand Spring Tour, and then rode the 18 miles home from the park by myself with that tire like that... So go check your tires!
Note to self: check mountain bike tires more than once a year.