1) They don't except manufacturer's coupons. Only there own Costco coupons.
2) Quantity of item you are getting, be sure to compare unit prices or price per ounce to make sure you are still getting a good deal. Check expiration dates, a lot of time you may not use the whole thing before it expires. You will probably be able to find better deals using coupons at grocery stores on many items.
3) You have to factor in the cost of membership, although I am sure there will be lots of promos and maybe even trial memberships, remember to factor in the cost of the membership in your budget to make sure it is still a good deal for you.
4) Costco is a danger zone for spending...you will never leave with one item, and since the items are higher priced since they are so large, it becomes very easy to spend hundreds of dollars quickly!
*And remember I have read more than once on other coupon blogs that coupon divas have "let their membership lapse"....
Do you use Costco? What do you think?