Ok ... here are some answers and observations:
1) The official free upgrade period lasts until July 29, 2016. You can do it anytime before then. Having upgraded 5 devices, I see no reason to wait. If you upgrade in that time you will continue to receive free updates as Windows 10 evolves through the years.
2) My tower desktop is possibly the best source for the comment on compatibility. I have a wide range of programs running and if they worked on Windows 7 or 8, they work fine in 10. I think any 32 bit programs that ran on XP will also work without any problems. I have not experienced one compatibility issue. Windows 10 does have a feedback ability, and if you do experience a problem, and report it ( detail really helps ), it may well be addressed quickly in the regular updates. We saw this happening throughout the Insider period which continues to exist for years to come.
3) Some people report issues with the upgrade, but I often wonder what it is about their computer that creates the problems. Reading the comments simply does not provide enough information. I tell people to keep running Windows Update on their current version until it reports no more updates ( after a reboot ). Then do the Upgrade to 10. I also suggest unplugging USB drives and turning off additional monitors while doing the update. That is not something Microsoft has said, but I feel it eliminates potential issues. I did that on my desktop and had no problems at all. When I turned on the 2nd monitor, it was instantly recognized and worked fine. The same was the case when I plugged the drives back in.
4) There is a lot of misinformation out there by people who simply did not take the time to read the Getting Started info, or to look at the options. The Microsoft Community Forum is filled with people saying "this doesn't work" until someone replies how to turn the feature on ( settings ), or how to use it.
5) Virtual desktops is new to Windows and well implemented. I don't use Linux, I use Windows, so its an addition I really appreciate. My comment was about it's usefulness, not some claim that Microsoft originated the idea.
6) You can get all the info you want here:
http://www.microsoft.com/en-us/windows but that is the US site ... I'm sure the same thing is available in other countries with the native languages.
I'm going to ask a favor here. I started this thread because most of us develop for Windows and we need to understand the OS on which most of our programs will run. I didn't post it to sing the praises of one company, or OS, over any other. There is often a tendency for people to hear "Microsoft" and start making negative comments. PLEASE DO NOT do that here. First, the company has made sweeping changes, and the "age of Satya" is different. The company deserves to be viewed as it stands today, not based on what may have happened in the past. So my favor is to ask that we stay focused on Windows 10 in this thread.
Tim