I'm running Debian testing since 4.0 beta and never had an un-bootable system or something got broken due to normal updates. I've just reinstalled the system once to migrate it to 64 bit, since there was no proven procedure to migrate a running 32 bit system to 64 bit.

There were rough patches along the way but, all distros were having the same problem in someway or another (vdpau, fglrx, multi-gpu support, ndiswrapper & wireless stuff, etc.) but it's a set it and forget it affair for a very very long time.

...and obligatory xkcd: https://xkcd.com/963/