I did this a couple times for limited edition systems. You just have to wait in line early and get as many as the store will let you.
It's not a tremendous amount of money but if you sell a few $300 systems for 2-3x the original price and you're a college student or such, it adds up fast.
The last time I tried doing it was for the limited edition pikachu 3DS; upon seeing a line of 50+ people in Oakland (most of which probably had the same intention as me), I decided that the gain was not worth it anymore.
I recall my friends doing this for the Wii back in the day. They put in reservations at GameStop and checked daily at various stores. I'd imagine it's the same way. You just have to get lucky sometimes.
