Most posters that have let their TCH get to empty (myself included) have noticed that there is 3 gallons reserve even after the miles to empty reading says "0". By stupidity I drove 10 miles on vacation after the "0" mark and took 15 gallons to fill up. Several posters (look at old threads or edmunds forums) and you'll see this discussed.

I don't recommend the practice of running on empty but it's not imperative that you worry about filling up when your TCH hits the quarter mark.