I am not quite sure about the particulars, but it seems that the Costco pass is a no brainer considering every other option in USH are quite pricey and not quite good. It's 90 dlls isn't it?? Someone has some insight about this?
One other minor note: If you have the Costco (or any other) pass and you're in the park on a day that front of line passes are still available, you can upgrade this pass at the park for the price of the front of line ticket minus $95. Not sure how available these will be once Hogsmeade opens, however.