I'm still a sucker for OS upgrades, especially free ones, so I upgraded both Windows machines in my home (one laptop, one PC) to Windows 10 soon after it was released. I just recently upgraded the laptop to Anniversary edition. Overall the OS seems functional, and loses the annoying Windows 8/8.1 start screen, but I'm probably not taking full advantage of the features. I was interested in using Cortana, but not so interested that I would tie my local logins to a Windows Live account. Why not let me use the Cortana features with a local login? It's not like I'm lugging my PC everywhere or replacing it like a tablet.
Also one minor comment about the Windows 10-specific options dialogs is that they seem to have a lot fewer options, so 99% of the time I just use the search bar to get to the Windows 7-style options dialog.
Now the main reason I wanted to post was three pretty annoying bugs. One was with vanilla Windows 10 (haven't seen it yet in Anniversary, but the upgrade is young). That is that the start button and widgets on the start bar would sometimes stop working. This ranged from mildly annoying (I can't set the system volume!) to basically dealbreaking (I can't do any work with NO start bar!) Sometimes a reboot would fix this, but sometimes it wouldn't. In the worst case, after trying a bunch of online remedies, I basically had to do an in-place reinstall. That worked, but that shouldn't have to happen for such a basic piece of functionality. Perhaps a more effective repair install that fixes the start bar?
The second annoying bug (again, in vanilla Windows 10, don't know if this was fixed in Anniversary), but my laptop tends to wake up from sleep in tablet mode. It's a Lenovo Yoga, so it can theoretically be used as a tablet. However, I practically never use it as such and never put it in the tablet "position," and yet I have to keep dealing with the initial disorientation of the UI not being what I expect when I open it.
The last annoying bug just started happening with Windows 10 Anniversary on my laptop. It seems like the pointer keeps jiggling nonstop. Now, I don't visually see the cursor move, but if, say, I'm watching Netflix in full screen, the player UI keeps popping up every second as if I'm continuing to move the mouse. Moreover, the screen never sleeps (I assume for the same reason).
I'm willing to put up with this nonsense (and foist it upon my poor wife), because I still have some fun fixing up OS issues (see many hours of toying around with Linux). But for my mother, I made sure that her system did not get the free update, because I thought there was very little gain for her in exchange for a lot of new issues.