Seriously, it almost feels as if there was somebody actively sabotaging things.
Disclaimer: I am on archlinux and therefore the packages are mostly "as is" from upstream without distribution patches to make it "nice". This is the raw experience I got from those packages.
1. Recently kdeinit4 would crash for me as soon as I start krunner.
2. KDM doesn't display the cinnamon session for whatever reason. Has really nobody tested this combination until now and seen that it doesn't work?
3. cinnamon-settings from cinnamon git doesn't work with gnome 3.4. "dbus.exceptions.DBusException: org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.SettingsDaemon.DateTimeMechanism was not provided by any .service files". If you fork, either do it right and fork every necessary component OR keep up with upstream.
4. gnome3 cannot set hotkeys with the windows ("super") key because it's apparently not a modifier key. But still it can set hotkey combinations with the super key to actions in the "system" tab i.e. the run dialog. In gnome2 the exact same bug report has been open for YEARS until someone actually fixed it to the behaviour every single other desktop environment and windowmanager I ever tested. Now in gnome3 it's apparently broken again and even the workaround to map "hyper" or "meta" to the windows key doesn't help.
4.1 It's extremely easy to crash the gnome background settings in gnome 3.4.1. Just open the dialog to add a wallpaper when the list is empty, but then cancel. With some luck the "-" button gets clickable. Click it. Crash it. If it was only a small project, sure, bugs can happen. In such a big project with such a big community - I don't want to know how many usability bugs I would be able to find if I was actually trying instead of just thinking "I wonder what will happen if I cancel this operation".
5. lightdm bzr doesn't set an appropriate environment by itself automatically as does every other display manager I have ever used. PATH is almost useless and the locale of the started session is of course not the system locale.
6. When logging out of a session started from gdm it just sits on a black screen and wastes 100% cpu time.
Today I encountered 1 and couldn't make it go away so I thought I'd try some alternatives. I was not even trying to find a bug, I was just trying to get the most basic usage out of it.
I sometimes wish xfce was ported to gtk3 and had its usability upgraded a little. And I sometimes wish we still had the equivalent of the desktop experience from Ubuntu 5.04.