I just bought a DH cake mix today and noticed (after I opened it) that the Use By date is 5/26/07. According to the DH site, Duncan Hines Layer Cake mixes perform best if used within one year of the manufacturing date. Other Duncan Hines mixes and frostings should be used within one year. This time frame is only a guideline. If stored in a cool, dry area our products will remain fresh longer. Older mix is not harmful in any way; however, the leavening ingredient is affected by age, and the product may not rise properly.
Should I use it? I have to make a cake tonight and I'm leary about these things.
... its more to give you an idea for when the date was years ago (and we all find that lurking box now and then). 
The dates on boxes are only guidelines and they are used mainly to help groceries rotate their stock (read this on the internet after and argument with DH a few months ago). It isn't that far out of date to make any difference. I buy dry goods that are out dated all of the time and have had no problems with them, have never gotten sick nor noticed an off taste. As long as the pkg is sealed it should be fine.
Val
ok I know this is about cake mix, but just an fyi for you all, incase you use pancake mix after the dates as well. I read somewhere( not sure where) that pancake mix will grow a toxic mold, that you may not see, and can potentially kill you. The article was talking about a mom that made pancakes for her 13yo or so son, and he ended up extremely sick from it. Now that being said I have eaten cakes that have been made with expired cake mix and it tasted just fine and I have'nt heard anything about people getting sick from expired cake mix.
I made the cake and it rose perfectly. I was freaked out about the pancake story but this made me feel better...
http://www.snopes.com/medical/toxins/pancake.asp
I made the cake and it rose perfectly. I was freaked out about the pancake story but this made me feel better...
http://www.snopes.com/medical/toxins/pancake.asp
I didnt mean to scare you, I've never heard of anything like that with cake mix but someone else was talking about using other items after dates, and I just wanted to give a heads up on that. I'm sorry for scaring you. That was not my intentions at all.
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