I've been a Linux user since 1994, and the Unix philosophy is an essential part of my lifestyle. The main reason I've used Linux is that it is simply the most productive way for me to get things done.
Since 2005, I've been an enthusiastic user of Ubuntu. At the time, and for several years thereafter, it was (IMO) the best Linux distribution, combining the careful design and usability of Debian with up-to-date hardware drivers and frequent high-quality releases.
However, for the past two years, using Ubuntu has been an increasingly frustrating experience.
The problem began with Ubuntu 7.10, which added Compiz. The precedent that was established by this release was that the addition of useless "eye candy" was considered an adequate justification for major regressions in functionality and usability.
At this point, I abandoned the default Gnome-based Ubuntu in favor of the KDE-based Kubuntu. Version 8.04, based on KDE 3.5, was outstanding. Yes, there were no fancy desktop effects. But everything worked.
Then came Kubuntu version 8.10, with KDE 4.1 as the default desktop environment. In terms of the sheer number of regressions in functionality and gratuitous interface differences, this release eclipsed even Ubuntu 7.10. The backport of KDE 4.2 helped somewhat. But I still spent considerable effort finding work arounds for software that was simply broken. For example, the very nice kpdf program for viewing PDF files was replaced by something called "Okular", which I suppose works OK unless you want to print, in which case you're pretty much screwed. Drag and drop between Linux and Windows XP (running in VMware player) stopped working. The mechanism for configuring panels changed drastically. I could go on and on.
I'm now pinning my hopes on Xubuntu, the version of Ubuntu based on Xfce. I'm now running the beta version of 9.04 on my laptop, and I'm cautiously optimistic, although I have not had any success connecting to the wireless network I use at work. (There appears to be a bug in scanning for wireless networks, and the dreadful Gnome network manager appears to be as buggy as it was the last time I looked at it.) I'm hoping that the release version of 9.04 will prove to be a stable platform. It's simple and configurable, and seems designed with usability in mind.
The evolution of Gnome and KDE, and hence Ubuntu, recalls the Second System Effect. Somehow maintaining a working, stable system is not sufficient, even though that has been the strength of Linux (and Unix in general) for many years. The developers responsible for creating the Linux desktop experience feel that it is necessary to make lots of crazy, unintuitive changes. To put it another way, both Gnome and KDE are beginning to feel a lot like a certain desktop OS from a corporation in the northwest US. And that's not a good thing.