Had a Costco membership for a while now, and after all the hype find it pretty much a waste of time other than the quality of the meat, most of which (like the chicken) I can't use because I don't feel like having to defrost it.
Their prices are at least as expensive as regular grocery stores, with the bonus of having to buy and store a huge amount. If you buy store brands of any items, they're much less expensive than Costco without the storage or handling of giant amounts. For name brand things, it's just not worth it to me to have to store two gigantic boxes of Cheez Its to save 20 cents, if that.
I understand how they run sales that can actually occasionally allow you to save money in exchange for buying a carload, but having to keep track of those and make a trip through the Who concert that is my local Costco to buy a box of dishwasher pods because it actually saves me a couple bucks, just doesn't happen.
We'll probably renew simply for the steaks, ribs and salmon, which are better than what we get elsewhere and well priced, and there are a few things that are a decent enough deal to grab when we're there, but not at all worth a special trip.