Philip Elmer-DeWitt at CNN Money:

By the time Christmas sales were over, Apple had shipped more than 15.4 million iPads and Amazon nearly 3.9 million Kindle Fires, passing the Samsung’s Galaxy Tab and Barnes & Noble’s (BKS) Nook to take the No. 2 spot in global sales.

It’s a pretty stark contrast. The source for this info is iSuppli, which I sometimes take with a grain of salt, but it’s an interesting comparison regardless.