1. Dessert topping or floor wax? Microsoft is trying to mash up two disparate interfaces -- traditional mouse/keyboard and touch -- in one OS. Tablets are notoriously bad at keyboard input, while PCs have yet to demonstrate more than minimal competence with touchscreens. Win8 will have to handle both equally well on both mobile and desktop devices to win acceptance.
2. Ribbons and Tiles and Metro, oh my! Win8 schizophrenia extends to software, mixing Windows Phone 7-style "live tiles" with the Office 2010 ribbon toolbar. Old Office hands say the ribbon makes them more productive, but newbies tend to run screaming in the other direction. Users will have to get comfortable with tiles that can be either live data streams, apps, or files, depending on where they are. Enterprises looking to make the Win8 plunge may be forced to plump up their training budgets.
3. Hardware gone wild. Apple, of course, controls everything inside its ecosystem, while Google now owns Motorola Mobility. But Microsoft still has to rely on hardware OEMs to bring the sizzle to its OS steak. Particularly with tablets, even a small difference in weight, thickness, or battery life can make a huge difference in the marketplace (see HP TouchPad, above).
4. Security, security, security. In the Decade of the Hacker, everything had better be locked down tight. Microsoft is much better about security than it used to be, but then again, it was awful. By virtue of market size alone, Windows 8 will have crosshairs on its back; Internet Explorer 10 needs to be more secure than Chrome, Firefox, or Safari for Microsoft to have a chance.
5. It's Microsoft, dammit. Will Win8 come in 2 SKUs or 12? Will users have to jump through hoops to document they own the copies they paid for? How many times has Microsoft shot itself in its collective feet over the years -- and how much more patience will the market have? Even a zombie will die if you cut off its head. Windows 8 may be Microsoft's last chance to sink its teeth into the action.
This article, "Windows 8: Microsoft's greatest comeback ever -- or its last hurrah?," was originally published at InfoWorld.com. Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest business technology news, follow InfoWorld.com on Twitter.