I calculate the unit prices in my pricebook as well. I've just started keeping it in Filemaker instead of Excel - more work to set up but I wanted to have something that let me keep long term records better organized. It's overkill - or cheap entertainment depending on how you look at it.
Before that I had one in Excel and it was at a time I was low-carb dieting. I ran an extra column that kept track of cost per 100 calories.
That was really useful and made it easy to compare the cost per equivalent food value of various meats, cheeses, eggs, peanutbutter, etc. I don't keep that as part of my price book any more, but do run a calc or two every once in a while - especially as the types of foods I buy change over time.
Lynda