(NASDAQ:AMZN) recently bragged about the performance of its Kindle device family over the holiday shopping weekend. Between Black Friday and Cyber Monday, Kindle device sales more than doubled compared to last year. Cyber Monday alone was the "biggest day ever" for Kindle sales, which includes both e-readers and tablets. Unit sales were boosted by Amazon discounting its original Kindle Fire from $159 to $129. For some context, Amazon sold roughly 4 million units last December. Apple (NASDAQ:AAPL) recently launched its iPad Mini while Google's (NASDAQ:GOOGL) Nexus 7 is a worthy rival. Microsoft (NASDAQ:MSFT) recently launched its Surface tablet, as well. Unfortunately, Amazon, Google, and Microsoft don't disclose unit figures, much to the frustration of investors.

Fool contributor Evan Niu, CFA, owns shares of Apple. The Motley Fool owns shares of Apple,, Google, and Microsoft. Motley Fool newsletter services recommend Apple,, Google, and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.