1st off came across this app which some might be interested in - it's free, it's for win10 only, it lets you set volume levels individually for each running app. http://www.neowin.net/news/ear-trumpet-a-windows-10-audio-utility-worth-checking-out
Updated a win10 64 in a VM & on my hard drive, with no major issues. Trying to (re)set the sign-in PIN did not work, & adding the Insider Hub app took forever in the copy on my HDD.
I have speculated that the win10 file system is a step towards the new file system Microsoft has been working on for years. If you go to run a disk check in 10, it 1st says you don't have to, but gives you the option to scan anyway. Checking the disk in another running copy of Windows 7 takes forever -- however it *might* be more accurate...
The 64 bit upgrade on my hdd left a bunch of corrupted files behind in C:\Windows.old\. Win10 gave 2 options for scanning the disk -- a regular version that said it would tell me if there were errors, & a repair version. I do not know if the 2nd option is similar to win7's "Scan for and attempt recovery of bad sectors". If it is, you don't want to run it on a NTFS disk/partition. For that reason I chose the 1st option which fixed 2 files -- disk check in win7 fixed them all.
I've got a copy of win10 32 on my HDD as well -- a recent addition I hope may eventually take the place of the win7 32 bit copy of Windows I use very occasionally. I'm half guessing, half hoping there will be another ISO released between now & the 29th -- I'm holding out for that build to set up a 32 bit VM, hoping that it works better than the latest build. [The idea is to eventually replace my win7 32 & 64 bit VMs.]
For now though, the 32 bit copy of win10 on my HDD would not detect the available upgrade build, so I went with the last ISO, which worked OK. It still would not detect the latest build however. That combined with problems just getting the 32 bit version installed are what makes me want to wait.