As disgruntled customers of those very retailers who are making the grand claims about queuing times know, there can be a significant gap between the rhetoric and the reality, the theory and the practice.
It is this chasm that a US-based computer installation company called Datatec Industries is aiming to fill.
Having already introduced retailers to a system that sorts buyers from browsers, the company has developed a product that it claims is able to forecast the number of people that will arrive at a particular checkout at any given time.
The New Jersey organisation says the Fastlane software package can "ingeniously predict, up to 15 minutes in advance, how many people will arrive, each minute, at the checkouts".
As a result, store managers can add operators for sudden rushes or - during lulls - reassign them to other tasks.
The package, which is currently being tested by three retail grocery chains, including Somerfield, has been used by such US companies as K- Mart for several years. But Britain is the first country where it has been used in supermarkets.
Joanna Schuller, the general manager of Datatec Industries UK, says this is because supermarkets in the US tend to run on lower margins and are less able to invest in technology. In addition, they have a tradition of employing bag-packers, which helps reduce congestion.
The Fastlane package - the first of an increasingly sophisticated series of software packages that the company intends to introduce in coming years - runs on a PC connected to Datatec's ShopperTrac counting sensors, which record each shopper entering the store.
It retrieves the entry times and - combining this information with statistics on the behaviour of shoppers - calculates the amount of time that each will spend buying, and thus predicts his or her time of arrival at the checkout.
The prediction is largely based on information collected via the electronic point of sale unit. By knowing such statistics as the number of items that an individual typically purchases, Fastlane can work out a minimum and maximum shopping time.
The company says the key advantage this offers is being able to deploy staff "proactively" - before queues start to build up. The traditional method of putting more people on the checkouts once somebody has spotted a build-up is, by contrast, reactive.
At busy times, such as Friday evenings and Saturdays, when all the checkouts are in use, the system can demonstrate that even more aisles are required.
The store obviously cannot build extra lanes, but Ms Schuller says the system will recommend that the store use staff as packers as a way of speeding up service.
"At least they know they need more people." She acknowledges that there may not be spare employees available.
This measure leads to a reduction in dissatisfaction caused by understaffing and in the arguably more important "walkouts" - customers who leave the store without buying, because they are put off by the length of the queues.
At Somerfield, a manpower planning executive, Jerry Marwood, says early signs are that the system is working well at its store in Willesden Green, north London, and the company is planning to test it at another site near Bristol.
Mr Marwood believes that the Datatec approach has advantages over other techniques designed to improve "labour utilisation", because it addresses customer service as well as cost control.
With retailers making bolder promises to their customers about levels of service, it is important that they have the means of making them happen. Datatec seems to be giving managers the "tools, ie, the information" that they require to enable them to deliver on their promises, he adds.
As this suggests, customer service is not the only beneficiary. Happy customers are likely to spread the news of the improved service - and so improve sales. But the system can also boost the store's performance in other ways.
"By minimising their `wait-in-line time', customers' in-store shopping time is maximised," says the company. And more customers buying more items translates, of course, into increased sales.
Finally, although the company obviously points to the advantages of avoiding unpopular under-staffing, the system also enables the store manager - with confidence - to shut down aisles in slow times and avoid "costly overstaffing".
Nor does the system need any involvement of staff. It basically runs itself, and employees require only about 10 minutes' training in its use.