Okay after my negative experience I’m now back to try Cinnamon, and I have a quite different story to tell.
First of all, thanks to Julian, I found that the issue I was having with the keyboard only involved my user’s settings, and not the code by itself. After a bit more fiddling around, I found a more detailed case where this happens.
My keyboard layout of choice is the so-called US Alternate International (us alt-intl); unfortunately even with the recent improvements in Input hotplug for Xorg, it seems like configuring Xkb on the configuration file, or on the directories, is not recognized by the evdev driver (at least), which is why I configured it with GNOME, Xfce, and, by reflection, Cinnamon, to change the layout of the keyboard — and that’s where the problem lies. When GNOME3 or Cinnamon are started, and they set the keyboard layout (both do it the same way as in both cases you configure it through GSettings), the Alt_L and Meta keys get somehow swapped… but not in all cases, as Emacs was still getting it right (which meant that just switching the two is not going to help me).
I guess I should track it down even further than this, but for the moment, I solved this by using setxkb in my ~/.xsession file, and that doesn’t seem to cause any trouble.
The other issue I reported, was that clutter is unstable when using nvidia hardware; to be precise, the issue is with nvidia-drivers (surprised?), and it’s actually the second issue that I find with their drivers in the last few weeks: the other was Calibre being able to get Xorg to eat so much memory that the system gets unresponsive, just by the sake of being launched, and add to that Skype that was unable to render *at all*….
So I decided to give a try to what Pesa suggested me to solve the Skype (Qt) issue: I decided to try the nouveau driver. Actually I wanted to try that a couple of weeks ago, but after reading through their website I wasn’t sure that my video card (NVIDIA GT218) was supported or if I had to deal with dumping the firmware out of the nvidia drivers and whatever else… but the other day, after screwing my own system over, and needing to boot from SysRescue, I found out that the driver they load is … nouveau, and it worked decently well.
So since this is weekend, and the time was right, I decided to give it a try — and the results are great! Clutter works fine, Cinnamon works fine, and while I haven’t tried anything that is running in OpenGL proper yet (no games), and Google’s Maps GL reports not working with this implementation (not that I care much), it works definitely well enough for what I usually do. I haven’t tried audio out on the DisplayPort connection, but it’s not like I’ve ever tried it before… Suspension works very fine.
And yes for now my experience with Cinnamon is terrific!