When I bought my laptop a few months ago they blocked it, immediately called me to tell me about it, and fixed it immediately.

Part of the problem is that Costco.com continually "re-asks" for an authorization on orders for items that take a long time to ship out (such as their laptops).

I was kind of glad they did block it, considering the practices of Costco.com (i.e. holding up some of my credit), and especially considering how "easy" (almost too easy) it was to buy a laptop off of a website.

Never had a problem internationally. But I ALWAYS call the issuing banks before I go and give all itinerary-related details so that they notate the account in advance.