For those who's status says "preparing for shipment"
From Cult of Mac,
Go to UPS.com’s tracking page
Select Track by Reference on the left side
Enter your 10 digit phone number in the Shipment Reference field
Manually change Shipment Date Range to 4/23/15 by typing it in
If the tracking info doesn’t show up, try changing the shipment date range to 4/24/15, 4/25/15 or some other dates. Other reddit users have pointed out that you need to use the phone number...