totally dependent on product.
I'm a smeller. Bad odor gets it thrown out.
Microbiologists friends in graduate school did a study for USDA on hamburger. found even when it was almost chocolate and smelled pretty rank that it (microbially) was OK. Of course that was back during pre Bad News E-coil days. There are bugs out there now that weren't here yet when I was at the university. As I remember back then, we wore dark blue robes with yellow stars comets and astrological signs, and tall pointed dark blue hats. Our chief research efforts involved converting lead to gold.
I get calls at work all the time concerning expiration dates. I know the product has not gone bad, but our stability testing says I must say that it is past teh expiratin date and we cannot guarantee it has not degraded.
So a word of advice - don't call the manufacturer and ask if you can use stuff past expiration. Those lawyer guys on TV want soomeone to tell you it's OK to use past the dating, because then he (the plaid jacket lawyer) wins the lawsuit when you get the runs and sue the manufacturer.