My MAC store here in the UK has advised me to call on the day at opening hours because it will sell out during the day (mind you they told me they can get just 1 palette... Say what?!!! )
If you pay over the phone it's yours! I would assume in the USA should be the same, if you call & pay straight away it's guaranteed!
Sometimes I just don't get MAC... Logic says you should have some stock for *at least* some costumers ... anyway i rather call at opening time instead of trolling the website loosing sleep & nerves because i never manage to get my stuff. 1 second it's there the next it's sold out