Had no problem getting the 20% off a 40GB PS3 in Milford, MA. Cashier saw that it didn't ring up, read the coupon carefully and agreed that it did not exclude the PS3. She then just entered the 20% off manually.
FYI, Wal-Mart claims to have it in stock, for $29 and change. With shipping, it comes to about $32 or so.
Now if they actually ship it when they claim they will, I'll be a happy camper.