I'm an old-school user so I'm not exactly Ubuntu's target audience, but for Ubuntu was bad about a lot of the older, lesser-used bits of Linux.

The two things I can remember were problems with NFS out of the box (outside having to install nfs-common, which I'm fine with) and apt-cache not displaying descriptions of packages. There were lots of other, minor annoyances that affected people like me but wouldn't affect someone who got into Linux desktops after, say, 2010. My memory sucks though so those are the two I remember. Yes, there were bug reports filed and yes, they sat in the tracker for years with no attention from Ubuntu.

I wound up back on Debian once I got old enough that I didn't care about being behind the times a couple years.