It appears that Best Buy will be stocking Wii systems today, as evidenced by its circular for this sales period. The advertisement promises shipments of at least 12 per store, but higher-volume markets are likely to see more than that.
It is possible that other large retailers will be receiving stock today, as well, and rumors are already flying about Circuit City and Toys R Us. If you are still in need of a Wii, today is the day to go hunting for one.
