I guess we are getting wildy off-topic, but my own personal experience is very different: on my main desktop i run bleeding edge everything (kernel, Xorg, glibc, etc.) and just this year i've been through 3 difficult Xorg breakages which required the identification of some prior version of Xorg and libdrm packages and the unrolling of other dependencies.

One of them was a 'black screen on login' kind of breakage. Xorg breakages typically take several hours to resolve because pre-breakage packages have to be identified, downloaded and the dependency chain figured out - all manually.

Current Linux distributions are utterly incapable of doing a clean 'go back in time on breakage, and do it automatically, and allow it even on a system which was rendered unusable by the faulty package'. This is a big bleeding-edge-testers handicap for any multi-package infrastructure component such as Xorg.

OTOH single-package, multiple-installed-versions packages (such as the kernel) are painless: i don't remember when i last had a kernel breakage that prevented me from using my desktop - if then it took me no more than 5 minutes to resolve via: 'reboot, select previous kernel, there you go'.

glibc is _mostly_ painless for me, because breakages are rare - it's a very well-tested project. But if glibc breaks it's horrible to resolve due to not having multiple versions installed: everything needs glibc. My last such experience was last year, and it required several hours of rescue image surgery on the box to prevent a full reinstall - and all totally outside the regular package management system.

Plain users or even bleeding edge developers generally don't have the experience or time to resolve such problems, and as a result we have very very few bleeding edge testers for most big infrastructure packages but the kernel.

Thanks,

Ingo