I don't spend as much time as you'd think doing this. Once I figured out my routine and established my coupon organization system, I now spend about 30 minutes a week plus about 5-10 minutes a day. I think it's totally worth that investment of time to consistently save at least 50% on my shopping trips.
As far as going to different stores, I am lucky to live in an area where there are several different stores all within close proximity to my apartment and to themselves. This makes it easy for me to stop at several different stores each week. However, I won't go to a store to buy just one item if I can buy that same item for $0.10 (for example) more at another store that I already plan on buying several items at. It just doesn't make sense from a time perspective.
Some stores, such as Whole Foods, are a little bit farther and out of the way for me. I only go to these stores once in a while, when there are a number of items I am interested in. I try to work the Whole Foods trips into times when I will already be going to somewhere nearby.
