Addressing the OP, I too have been running the Technical Preview in a virtual machine almost since the day it became available and am now running build 10041.
All of my "Important", (to me), software has run fine on it so far, I haven't had a chance to install any on the latest build yet but I don't expect any nasty surprises.
The interface, particularly the Start Menu/App residence/Start Screen.....thing, (what DO I call it?), is....better. That's not fair, it's much better than the horrid Start Screen in Windows 8. I just plain don't like the Metro Icons. But the menu is back and I can remove some or all of the Metro Icons, my choice.
I'm not a big fan of the new folder icons. But again, they're fine.
If Windows 10 ends up as fast and stable as 8/8.1 then I can't ask for much more in that department.
Yes, other than the UI I think 8/8.1 is a very good OS. It boots fast even with Fast Boot disabled, runs every piece of software I've thrown at it and has never blue screened on me.
What has me wondering is, why is MS giving it away? Purely PR?......
......Microsoft?.........Really?
First, I think the whole Windows 8 Start Screen/App thing was a way for MS to get us to sign up for and use their apps and products, sort of force their way onto our computers.
I also know they've been trying for years to get us to embrace a subscription model for MS Office. Is that what they have in mind for Windows going forward? Or will they try and make money on selling us their products? Or will it be advertising? Or, more likely, a combination.
In any case, I don't for a second believe they're going to abandon trying to monetize the largest installed Operating System on the planet, or "Giving" anything away. There has to be something else involved.
I wonder too about delivery. As I understand it we'll be able to install it as an upgrade through the update process, sort of like Service Packs. But what about folks who'll need to do a reinstall. Will they have to reinstall their original OS and then do the upgrade again? That's what we've historically had to do with Service Packs if we reinstalled from a disk that didn't include the SPs.
But, we've also been able to download those Service Packs and install them directly or even slipstream them with our original Windows disk. I still have XP, Vista and Windows 7 service packs somewhere.
Well, those are just some of my thoughts. I'll probably be proven completely wrong..............