I do a one month, and YES I stick to it. My menu for July was in this thread: http://www.mothering.com/discussions...highlight=july
I'm doing something a little different for August. I know from experience that we pretty much eat a lot of the same stuff every month. So what I'm did was shop around for the cheapest price for staples (whole wheat flour, whole grain rice, dry beans of different types, common canned goods, etc), and figured out how much it would cost to buy in bulk (flour 50#, beans at least 10# I don't remember exactly), then I priced around the cheapest meats from the sale papers (found chicken for 39c per lb!!). Came up with a total price on this stuff (I think it's $132?) And I will plan an August menu around that.
Usually I planned before buying, and didn't buy based on sales, but for August I'm going to buy first then plan, based on the cheapest prices. And I'm sure the staple items will actually last more than 1 month, and I'll just look for another meat sale in September. Now, that only leaves perishable items to buy, like fresh produce, eggs, milk. (Except figuring out how much to buy at one time BEFORE making the meal plan comes with practice and experience, based on what we usually eat in a month.)