When has your food really gone bad?

Before and after the New Year, I did a major cleanup of my home, vacuuming, washing floors, getting rid of old stuff, etc.  I also went through the fridge and all the cupboards in search of expired food products.  

Although it was incredibly easy to throw away fruits and vegetables that had morphed into gross squishy lumps in the vegetable compartment, and toss out old rice balls in the freezer that had suffered massive freezer burn, other products weren't so clear cut.  

When are packaged beans unsafe to eat?  Does it make a difference if they are in a carton or a can?  Preserved with salt or konbu?  Does mustard actually go bad?  On the one hand, I don't want to waste something that is still edible, but on the other hand, I'm afraid of invisible mold.  And what do you do with things that don't have an expiration date?  I have two jars of mustard that never came with a printed expiration date.  

Sometimes I feel that I waste too much time worrying about expiration dates, but I can't help remembering that one time that I accidentally ate moldy jam.  I wished that I'd either checked the expiration date, or the inside of the lid, before I'd eaten it.

~ Samantha