I installed W10 on my desktop Dell, yesterday. Install took just over an hour. As usual, several reboots.
From the way things look, the free W10 upgrade is probably a mime that sits on top of W7/8. There are notifications on MS's web site which state that you can do a "clean" install at a later date. I don't know how many folks will bother with the clean install as long as the "free" edition works.
The upgrade looks a bit like previous versions with its scrolling explorer panel.
I ran Adobe Photoshop Elements after the install, and did notice that the editing process was a tad faster than with W7. This is probably due to more efficient software program execution on the new platform.
If you have a newer Dell laptop that uses NVIDIA video drivers, it appears that the compatibility issues weren't resolved until right before the July 29th roll-out. I previously visited NVIDIA's web site, and no driver upgrades were available as of July 28th. I have two lap tops that run W7 and W8 respectively, and neither one got the upgrade yesterday. I'm waiting on my "invitation" for both of them, now.
Stay tuned.