Still not sure...
But I did do the upgrade on my Thinkpad w/ Win7 yesterday. Interesting process.
First, it took all day. Seriously. 3Gb download takes a while on my slow DSL. On the first attempt, after a couple hours I got an error. There was a link in the error message. It took me to a clear explanation that said I needed to include three internet IDs in my firewall exception list.
I figured that was probably in Norton, so looked around and couldn't find anywhere in Norton to do it. Then I checked Firefox. Found a place and put the IDs from the error in there. Back to W10 update and restarted it.
Another couple hours and another error. Said it would have to remove Lenovo Rescue & Recovery. I had already read this would have to be done, so said OK... and it restarted.
Another couple hours and got the Oky Doky message... ready to install. Told it OK and it started. Fired up the grill, cooked some hamburgers, ate, cleaned up, and the installation finished... about an hour.
At the first boot, a screen came up touting about a half dozen new and improved things Win10 would do for me. Thankfully I took my time and read them. Just about every one included a statement about sending my data, browsing history, location, etc to Microsoft. It would reset my default browser, music player, movie watcher, etc. There was the familiar NEXT button at the bottom, but hitting it accepted all these things.
In smaller print at the bottom was a "customize" selection. I clicked on that, and it easily let me turn OFF each of the new features. I got 2 or 3 pages of these new offerings, each w/ a NEXT button and a smaller "customize" button. I did customize and turned off
everything it wanted to do.
Finished, Win10 came up and looked almost identical to my old Win7. Everything seems to work, and honestly very little effort to get used to new OS so far. Good job by MS.
So my summation is: Plan all day for the upgrade, but it seems to work fine w/ minimal differences in appearance, (if you say "no" to all the new stuff).