LPT: if you order something from Amazon through Prime with guaranteed two-day shipping, and it doesn't arrive in those guaranteed two days, email Amazon customer service and request your free 1-month extension of Prime. I've gotten three free months of Prime so far this way. Here is the note from Amazon that I had found somewhere on their website a few ages ago:
Note: If you received free shipping through Amazon Prime, you may be eligible for a free one-month extension when the promised delivery date isn't met. Prime Extensions are limited to one per free trial and 12 for an annual membership. Free Amazon Student Memberships do not qualify for this extension.