What's the catch? The eval runs for only 90 days. When your time is up, Windows 8 drops into the same punitive mode that Microsoft uses for counterfeit copies of its operating systems. The desktop background fades to a permanent black, you'll see constant on-screen messages that the operating system is not genuine, and the machine, whether physical or virtual -- shuts down every hour.

In other words, it's completely useless.

On the bright side, if you download and install the trial today, you can use it through Nov. 13, 2012, long enough to get a good feel for the OS, or how it really runs on older hardware, such as a Windows XP or Vista PC, like Microsoft claims.

Can I upgrade the trial version later? No, you can't.

Microsoft makes it clear that the 90-day evaluation is a dead end. "It is not possible to upgrade the evaluation to a licensed working version of Windows 8," the company says on the website that details the trial. "A clean installation is required."