Dates marked on products are usually meant for the retailer, informing them when to remove stock from their store shelves. Most packaged foods (canned and dry goods) will likely be safe for consumption approximately one year beyond the "sell before" dates on packaging. Sometimes there are stamped markings on canned goods such as "Best used by 04/2011" but not all items in your cupboards will be as clearly marked.
When I inventoried my pantry in January of 2009 I labeled goods with an "8" to indicate that I had purchased them in 2008. Only a few goods failed to be consumed in 2009 from my 2008 purchases. I will not be returning these older items to my pantry shelves. I plan to use them up when preparing my meals during the month of January 2010. What I haven't used by then will get tossed.
Labeling your pantry goods for the first year will like take extra effort, but if you make this an annual chore in the years to follow it won't be that huge of a project. I initially tried labeling cans and packages by the month purchased. But, this involved either labeling items every time I shopped at the market, or shuffling through the pantry once a month. Too much trouble. Doing an annual pantry inventory works best for a busy life style. If you can keep your pantry inventoried weekly, or even monthly, my hat is off to you!