I have a pricebook. There are three stores in my town...IGA, County Market and a Sav-a-Lot...I also write down prices from Aldi's, but don't get there much as it's 30 miles away, but will make a point to stop there, if I'm in town.
It's helped me greatly, and has honestly become like a religion to me. Everything I buy gets written in the price book and where it was bought. I know where the cheapest places are to get all of my neccesities, and have even been known to swipe the reciepts from my grandmother or mother to write down the prices from that too.
I always insist on knowing the prices of EVERYTHING!!
However, it's convienent for me because I do my grocery shopping in one big circle...Sav-a-lot first, then I hit the sales and the things that savalot doesn't have at the other two. (I'm also a really big fan of the saturday flyers that come in the mail, listing the sales for the following wee.) Sav-a-lot is the farthest from my house...a whole whopping 12-15 blocks maybe!
Another thing I've noticed with the two branch stores here in town, is that the best sales are at the end of the month...when social security is running out or food stamps are running too low. Then, those people don't have the money to shop, they can have their HUGE sales and make good impressions, but really, not near as many people are shopping, so they're not losing the money. But, if everyone were to wait til the end of the month to do their shopping, the sales are better.