About twenty years ago, Siobhan and I took the time to go through the supermarkets in the area, figure out which had best prices on each item we regularly bought, and make a list of what we typically needed sorted in order by the aisle in which they appeared and listed in whichever store had the best price. It took a few hours, and it would have to be periodically maintained. But every shopping trip from then on, we saved both time and money. We saved money obviously by getting the best deal, and we saved time by being able to zip through the store going straight to the next item we needed, as well as by avoiding that "extra trip" every few days for something we forgot (since going through the checklist before each trip ensured we caught everything we'd need virtually every time).
Somewhere along the way the paper list was replaced with a list on a handheld device, a PalmPilot at first, nowadays in ListPro on my Windows Mobile phone. This makes it a lot easier. Maintaining the list on the fly in the store when I find they've moved things around is as easy as drag-and-drop. And that process before the shopping trip of going through our regular items and picking out what we need this time is as easy as checking things as I scroll down (we typically do this in the car on the way to work, time that would have been wasted otherwise).
During the last twenty years, people who've noticed how we do this have reacted with varying degrees of incredulity. Generally the reaction is surprise that we'd put so much time into it, which is bass-ackwards: spending a few hours one day will save time every week for years to follow, so it's a large net savings. (Though people often don't believe this. They imagine that that "quick stop" they do every day or two on the way home doesn't add up to anywhere near as much time as it actually does add up to.) They often doubt we're really saving any money by splitting our shopping between multiple stores, or that we're doing it by settling for cheaper versions of products than they would (which of course we might be in some cases, but whether you're buying store-brand or premium, either way one store might be cheaper than the other, so that factor cancels out).
What's really interesting though is that, with the growing ubiquity of smartphones, more and more people are gradually starting to employ some of the same techniques. I saw someone today using an iPhone shopping list program as she went through the aisles, and I caught a glance at her list. Like mine, it's organized by aisles, but I couldn't tell if it had a checklist of common items that's used to easily make the "what I need today" list, or whether it was good at supporting multiple lists for different stores (and moving stuff between them). If she isn't using those features, I bet after she's been using her iPhone for this job for a while, she'll start wanting them, and find an app that can handle them.
This is still a long way from the ideal where a piece of software doesn't just help you organize your trip, but also helps you find the best deals. But this is more about the process than about the technology. As with many things, shopping is a task where it's very easy to not realize where you're spending your time or your money, and so to not recognize ways to save either. Far simpler to fall into the habit of making a lot of quick convenience trips, and even those who avoid the trap of convenience stores still tend to let the supermarket and their schedule dictate their shopping habits to their detriment. The technology is noteworthy here only because it might nudge people out of those habits as it gives them a reason to think about doing things differently, causing them to almost by accident find new efficiencies. And that's good: if they give credit to technology for causing efficiencies that it didn't really create, that'll go against all the times they give blame to technology for causing inefficiencies that it didn't really cause.