Just bought 2 Wii U, 1 used from Amazon warehouse deals (30 day return) and another refurbished from Nintendo directly (no returns but 2 year warranty).
Amazon = 5.5.1
Nintendo = 5.4.0
The one from Amazon was in rough shape. Scratches, bent/worn cords, loud optical drive. The one from Nintendo looked brand new, not a mark on it, with a quiet optical drive. Also came with a game and literature. Easily upgraded to 5.1.1 for better homebrew with Paper Mario Color Splash retail disc. You could even walk into GameStop and ask to borrow a copy to upgrade with it or just "rent" a used copy and return within 7 days for full money back.
Order from Nintendo before the stock is depleted. Both units sold for $200.