5-6 years ago, I bought into the ubuntu promise of being a better debian before ubuntu was cool, and switched my main laptop from debian to ubuntu. At the time, ubuntu made sense: it was supposed to be a professionally maintained debian with freeze and stabilization every 6 months, and would contain binary drivers that debian wasn't willing to ship.
For the first year or two, I was happy with ubuntu, maybe all the way up to Gutsy or Hardy. It delivered on what I signed up for. But then, came a quite unfinished upstart, network manager suckage, non working pulseaudio for many releases, and an ever increasing amount of half baked crap.
Ubuntu switched from a better debian to some experimental distribution where shippping known broken stuff was ok, and even pushing experimental known unfinished stuff in an LTS was apparently ok. It became as bad or worse than Fedora Core, except Fedora Core never made a promise to be stable or make rational and generally 'safe' choices.
First, I started writing about it, and contacted several people at canonical to let them know how bad the non gnone non desktop experience was getting (and actually even the gnome/desktop experience was riddled with bugs), and after a few years, I eventually gave up and decided that enough was enough and switched back to debian, which is also what I'm doing at work (their loss, that's *many* machines):
Intrepix, or when ubuntu started breaking linux networking with network manager
Jaunty, or network manager still being horrible
Hardy apparently was the last reasonable LTS.
Karmic, finally had network manager working, but brought pulseaudio to make sure you couldn't play sound anymore
Lucid, brought the wredged plymouth. That was the day I decided that I was getting tired of ubuntu, and got really pissed when I learned that they knew plymouth was broken, they knew no one wanted to test it, so they put it in an LTS and made it required with the system to make sure you couldn't remove it. Fsck you very much canonical, that's a good way to end up on my shit list.
Maverick, plytmouth still wasn't working and still couldn't be disabled. Also, it had virtually no documentation still. At this point I was fed up enough that I called it "plymouhtn is the worst thing that happened to linux", but I take this back. Maverick is really when I got pissed at canonical for not fixing their clusterfsck from lucid and not reversing their aweful decision to just shove unfinished crap in the distro.
Natty? I just got tired of breakage, didn't even upgrade to it.
Oneiric? I didn't write about it because I didn't keep it long enough before replacing it with debian. It wasn't horrible, but didn't bring me anything new that was worthwhile and broke network manager for me again. Oh, and for fun, you couldn't really upgrade from Maverick to Oneiric anyway, you're supposed to install each and every new version unless you jump from LTS to LTS (this is simply because Canonical chose not to support that, which is in their right, just like it is in my right to then not be interested in using it anymore).
At this point I drew a line in the sand, and decided to switch back from Ubuntu to Debian. Debian doesn't have an agenda of pushing half baked software or disruptive software to its users, and does its very best not to break compatibility, at least needlessly.