I suspect there is much to be done to optimise supermarkets; there are three key problems: finding goods (with subproblems of knowing whether goods are stocked, knowing whether the goods are in stock, and routing); aisle congestion; and checkout congestion.
The low-tech solution is better sign-posting, but there are so many types of goods in the average supermarket (let alone hypermarket) that detailed sign-posting would be counter-productive - it would be hard to find the right sign.
The high-tech solution is a digital store map, accessible by smartphone with voice recognition location search. The next step beyond this is a Sat Nav style display (or docked smartphone) on the shopping-cart that maps out a route in-store based on the items in a list (downloaded from online account).
A simple fix to aisle congestion would be narrower shopping-carts, as this would allow more shoppers to pass each other on the aisles. However, this could reduce the amount people purchase, making it an unattractive choice for supermarket owners.
Another possibility would be to monitor store traffic and aisle congestion, for example with pressure-sensitive floors or 3D imagers such as Kinect. Data on which aisles get congested could be used to rearrange stock. This should also mean that shoppers visit more aisles on average, which increases their exposure to products - something which would be attractive to supermarket owners.
There are numerous solutions to checkout congestion: self checkout; in-shopping-cart self-checkout; near-field-communication-based checkout; etc.
For classic manned checkouts, monitoring people entering the store, combined with knowledge of the average visit length, should allow supermarkets to predict and preempt checkout congestion (i.e. upmanning in advance of an anticipated period of congestion).
A solution to overall busyness would be to publish store visit data, allowing customers to easily identify when the store would be quieter, and tailoring their shopping plans accordingly. This might benefit the supermarket in requiring less staff overall, as busy periods would be smoothed out.