It really depends on what you mean by replace. If you want to use it for email, Word Processing, Net Browsing, listening to music, etc. It is fully competent. I run Linux as my main box at home - and the above is what I use it for.
At work I have a Win 7 box that I use VNC to talk to Linux servers to engineering work.
If you want it for gaming - not the right platform. If you want it for video editing - not the right platform.
Finally - if you want Windows functionality - then use Windows! I’ll admit that Win 7 is the first reliable version I’ve seen since Windows 3.1! However, the guy was talking about Windows 8 - which is a NEW Bird altogether, and the advice to stay away from it for a year is well advised!
Lastly - something you ignored is that there is at least one version of Linux that your arguments mostly fall down on, and that would be Android ;-) It has 1 BIG Guy behind it, it has a stable interface, and the development platform is stable as well. Consequently - for total number of “seats” as it were... Linux beats Windows just because of all the phones it’s installed on ;-)
Windows 8 has been already for about a year, in developer version, and consumer version, and in prelease version. And, more than 10 million people, including development testers, have used it, for many different functions, and some people, including me, had it replace Windows 7 completely before the official production release last week.
Most of the negative had to do with the “Metro” UI, with many complaining about the colors and how ugly it was. But, myself, I never encountered performance issues, and none related to hardware. Now, with Windows 8, it’s even better than the preview versions, and much better than Windows 7. I can’t conceive of a reason why I would ever go back to Windows 7, or any other OS.
When it comes to Android, I did mention it in one of my previous posts in this thread. People don’t use Android as much as hey do the devices in which it comes pre-installed. To most people, the way the device works, is part of the design, and they don’t separate the hardware from the hardware. To most, it just works, just like a washing machine works, and people don’t have to worry about the inner workings. With a more productive machine, like a computer, people are aware of the OS and it’s features. Therefore, people do have to make a choice for what goes inside those more capable machines. On smartphones, people don’t conceive of the problems, if any, as being OS related, though the more technical will know the difference. When people purchase a smartphone, they either purchase an Apple device or an Android device, without thinking about the underlying OS. Samsung doesn’t have to inform people about the OS, although it’s undoubtedly mentioned in the instructions manuals. People just use those devices as if they were just hardware that respond to keyboards and screen touches, etc.
However, now that people are beginning to discover that, Windows 8 phones will come with the Windows UI, they’ll have to choose about which phone to get, because, they choose will make for much different user experiences. Upt till now, it’s been a choice of providers of service, with the device choice being secondary in a lot of cases. Now, people will be making a more informed choice about OSes, and complementing them with the OS and other software. The OS inside a device, no matter what he platform or form-factor, will be something that people will have to know something about.