So, I order a new pair of shoes from Zappos. Good price, free shipping. But Puma's fit me weird, so I order the size I normally get. Later in the day, I just happen to see the same shoe for sale in a store. So I try them on and realize, holy crap, I need a half-size smaller. But then I forgot about it until like 9:00 pm. So at 9:00 pm, I call Zappos, and tell them I placed an order earlier and need a half-size smaller. They tell me it's not a problem.
So I get home from work the next day, and my shoes, in the size I requested not even 18 hours earlier, are at my door.