Why do I upgrade? That's the question that I've asked myself for at least the last four versions. I spend six months ironing out all the trouble to the point where it mostly works then I upgrade and start all over again.
A year and a half for my mic to work, USB drives that transfer at absolutely crawling speeds (solving in Koala for the first time ever tho!), disk to disk transfer at an absolute crawl (seems much better in Koala), flickering screens, disappearing mouse cursors (happens every time on bootup in Koala - a simple CR in any terminal window brings it back), and a host of little this and that's.
The worst issue though by a mile has been sound. There is always a problem with sound. Without exception. I almost had my sound working perfectly in Jaunty but now something is glitched in Pulseaudio or Firefox or Alsa or something cuz padsp now won't wrap around Firefox.
Ya know, I bought an original sound blaster for a 286 in '89-90 and it blows my mind that something like sound can be such a problem 20 years later. Everyone really needs to get on the same page.
Anyway, despite the problems I continue to use Ubuntu. It still seems the best for my needs out of all the distros that I've tried. And I'd certainly still be wasting far more time in Windows dealing with the anti-virus and mal-ware nightmares that are found there.
I'll keep using Ubuntu. And although I'll probably keep asking myself why I upgrade I'll still do it. ;)