I recently (two weeks ago) decided to finally switch from Windows to plain Ubuntu as a daily desktop. I'm well experienced with it from managing servers and have used it occasionally at a desktop in the past.
I've had - and continue to have, a ton of minor and a few large problems.
First, wifi. Apparently there's often problems with Intel killer 6e laptop cards, which required me to enter loads of console commands that I didn't understand to fix. I did finally fix it, but I'm not sure exactly what did it. A couple of hours work over a few days to fix this.
I work from an external monitor plugged into my laptops HDMI port with the lid closed, and it seems Ubuntu is massively confused by this. I'm constantly having to open the laptop to get a login screen to show, then logging in and closing it, then opening it again because now the desktop doesn't show.
My laptop screen resets to minimum brightness every restart.
I did a driver update and suddenly my external monitor wasn't recognized at all so I had to roll back.
And at least several hours more on other issues. Oh yes, if I suspend then try to wake, I get a black screen or occasionally the Ubuntu startup screen but can never get back to the login screen until I do a hard reset.
The Bluetooth audio was set to headset quality (mono) and the only way to fix this, following 20 minutes research, was to install a different audio settings app.
All of these things, I can fix. I don't want to, but as a technically savvy user I can do it, with enough hours put in. But there's no way I'd suggest anyone else in my family or friends to use it unless they clearly tell me that they would enjoy tinkering with their operating system.