I have no idea where I read or heard this sneaker tale, so to get to the bottom of this issue I called a friend at Jack Rabbit Sports, a favorite NYC running store, and a great resource for running information. While they were adamant about replacing shoes based on mileage and wear (yep, that 350-500 miles rule came up again), they see no problem with stocking up on your favorite pair of sneaks. In fact, according to Jack Rabbit, "Keeping a new pair of shoes in the box for a few months will not affect the performance of the shoes."
That is excellent news for me, and anyone else who loves a good deal. While it's important to make sure to choose the proper running shoe, once you've found a pair you're comfortable in, it's OK to grab a second (or third!) pair to stash in the closet. Just be sure to try each pair on, even if it's the exact same shoe, since the manufacturing process may cause slight differences in each pair produced.