Although it is notably less feature-focused than previous iterations, Snow Leopard's low price has it flying off the shelves. Market research firm NPD is reporting that the latest version of OS X is selling twice as fast as Leopard and nearly four times faster than Tiger. Analyst Stephen Baker called the upgrade's affordable price a "win-win for Apple computer owners."

Apple is selling both the single-user and five-user pack of Snow Leopard for $100-plus less than its predecessor according to Baker, showing that aggressive pricing goes a long way in a weathered economy. Baker noted that it will be interesting to see how Microsoft's (more expensive) upcoming Windows 7 fares in comparison -- something we're all looking forward to, I'm sure.

Earlier this year, Piper Jaffray analyst Gene Munster estimated that Apple would ship some five million copies of Snow Leopard during its launch quarter. While that figure seemed a little on the optimistic side at the time, it's far more plausible now. Leopard sold over two million copies on its first weekend at market, so if Snow Leopard is selling twice as quickly, five million units shipped seems likely.