Just chiming in....
we really like/love our Costco membership.... and we have to drive an hour each way to the ONLY Costco in our state.
I don't buy many of the cleaning products any more because I prefer to make my own (for health/environmental/cost reasons), but when I did buy their environmentally friendly "free" laundry detergent, I thought it worked well.
Our standing Costco list includes the dried mango (for DD), the Kirkland organic chocolate milk boxes (for DS), fish oil and other supplements (for DH), organic milk (although we can get it just as cheaply at Market Basket without having to buy 3 half gallons at a time), plain greek yogurt, sardines (for DH), almond butter (Marantha brand at a FABULOUS price if you don't mind the big jar), himalayan pink salt (best salt we have EVER tried), cinnamon (we use a LOT around here), Fancy Feast cat food (mostly when they are offering an in-store coupon....otherwise I can usually do just as well at Target with a sale/coupon combo), some meats and cheese, low carb tortillas, fresh fruits and veggies (grapefruit is a great buy this time of year), mixed nuts and peanuts, and the occasional take-and-bake pizza. The rotisserie chicken is a great deal, but unless we time it just right, we aren't there near a meal time and it is cold by the time we get home anyhow.
DH insists that we spring for the higher level of membership (business??) that pays us back every year. That rebate pretty much pays for our membership renewal every year, so I figure it is worth it.
I don't think that we are the "typical" Costco shopper... I don't buy many convenience/frozen foods (burgers, chicken breast, frozen pizzas, frozen desserts, Lean Cuisine multi-packs), we don't buy booze or soft drinks, I don't buy books, DVDs/CDs or magazines and VERY FEW cosmetics. I don't buy many soft line products either (sheets, towels, kitchen stuff), although DH has bought some jeans and some dress shirts and been happy with the quality. We have used their photo service a few times and found it to be a good deal. We have also rented cars online through the Costco website and gotten a VERY GOOD rate (and I shopped around a LOT!).
They are FABULOUS about returns!!
The ONLY thing I really hate about Costco is the fact that they will only accept cash, debit cards, or their own Amex card. I would LOVE to use my Southwest Airlines card and get air miles, since I usually drop $100-$300 every time I shop there. And they do NOT take coupons.
BTW, the frozen yogurt at the snack bar is DELICIOUS~

HTH..........P