I had a Windows 10 ready PC running 8.1, I had been deferring the update until it gained some stability, but a few days ago I took the plunge as I was being nagged to do it. It went relatively smoothly but there were a few issue to report some of which took quite some sorting and some unresolved. I am a retired IT professional so have some skills in the area, but how some people get on may be an issue. I am running all updates and am at Ver 1511 Update 10586,104.
1) Some desktop app shortcuts did not migrate to the 'All Apps' start menu item. Even new installs may fail to register correctly in the Start Menu. I've never seen the like of this before and have been using Windows since 3.1. Upon research I note many people have had the issue and there are claims that the number of shortcuts could not exceed 512. But I only have 200 according to the powershell "Get-StartApps | measure" command. I checked that all the shortcuts were correctly located in the "C:\ProgramData\Microsoft\Windows\Start Menu\Programs" directory and compared that with the "all Apps" in the start menu. So I had to make a workaround, using technology dating back to Windows 3.1. I made a folder, "Missing Menu" copied the missing shortcuts into it and pinned the folder to the Start Menu. I then realised that there might be some similarity between the missing items. A program's uninstall shortcut is usually missed... OK understand why this might be as you should uninstall from the Control Panel, But two shortcuts to executables that failed to register were non-Microsoft Utilities (Malware Bytes and CCleaner). I thought failure might be due to the fact they need Admin privilege to run. But it seems Microsoft might be 'Blacklisting' some apps. So I renamed the executable, created a new shortcut, copied the shortcut to the StartMenu folder and yes they appeared in the All Apps menu. .. Suspicious ?
2) MS seemed to have overlooked people like me who are running a desktopn, ethernet connected, with no GPS. This is a problem because my OS calculates my position from the IP address locator as it cannot use WIFi locate or GPS and so it thinks I am 50 miles south or where I actually am. There is no way to manually set my location so Maps and Cortana (locally based info) are useless. There are many other people moaning about this, and I have been told to install a 3rd party app, from an untrusted source to work around this. NOT an Option.
3) It took me a long time to resolve my default "save to" document location. My data is on a different drive (D:) to Windows (C:). My data was at "D:\users\NAME\" folder. I changed the settings under storage which does not have an option to select a rooot folder just a drive letter. So when I tried it created documents by default at "D:\NAME\". I have to change when I open a new app for the first time.
4) As Edge is not compatible with many websites and has other issue, I use IE browser default not Edge. I clicked on outlook links and they kept asking for confirm of which browser despite default set to IE. I fixed by add reg key using auto tool at https://support.microsoft.com/en-us/kb/3094186
Windows 10 seems like a good upgrade from 8.1, particularly if the above niggles are resolved. I hope this information helps others with any issues like mine and if anyone has any suggestions to help with the above please post a reply as I'd like to tidy up the bodges I have made.