I'm in the "when in doubt, throw it out" crowd. Visually examining or even smelling or tasting something may tell you whether it still tastes good, but that won't necessarily tell you whether it's bad. For example, botulism toxin is invisible, tasteless, and odorless but potential deadly in even small amounts.
One bit of advice -- check the dates at the store. I can't believe how many people simply grab and run, especially since I often find items past the pull date or expiration date. Often the items at the front of the shelf are older than the things behind them, but not always, so check.