I think Costco really shines when buying generic, bulk items like rice, flour, oil, etc. The other thing I think they do well are organics, b/c they allow our family to eat more organics than we would otherwise be able to afford at the local grocery store, i.e. frozen veggies, milk.
With that said, I have never found their prices on electronics like computers or cameras, etc. to be competitive, nor it is a good deal to buy heavily pre-packaged stuff from them, like individually-packaged crackers, nuts, dried fruits, etc. for lunches. But then, the pre-packaged higher costs also hold true for the regular grocery store, and while I try and stay away from heavily processed and packaged foods in general, we do need and use them occasionally, and when we need 'em, I do tend to buy them from Costco so I won't run out of them anytime soon, forcing me to go more frequently to the store (and inevitably, spend more $ b/c of it!)
Am I the only one who has trouble taking advantage of Costco's bulk produce? Although I have a largish family, we only own one refrigerator, and I simply can't store more than 1 or 2 bulk produce items from there, so I don't even try. I am much more likely to buy bulk dry or paper goods or frozen items b/c I have the space to store those. Perhaps if I went to Costco more frequently, I would buy more produce from them, to replenish what we use up, but right now we only go once every 2 months, again, partly b/c to help our budget (if I don't shop there every week, I can't spend too much $ there, right? Well, it's true in theory, anyway... :P)
Guin