IIRC, I’ve been running Debian GNU/Linux on my primary workstation since summer 1995. All that time (almost 11 years!) the operating system ran without any single reinstallation, starting with the Debian 0.93R5 version and ending with mixed sarge-etch (post-3.1). I only performed upgrades, I’ve never reinstalled the system from scratch. None of the upgrades required immediate reboot as used to be (or even still is) required by some other operating systems. The system survived all the upgrades (including numerous development versions), kernel failures, user failures, experiments, hardware changes, etc. running daily or even 24 hours/day. Such a stability is exceptional and it proves that stability is indeed one of the primary Debian features and that Free Software is a very stable and future-proof platform.
The operating system is being reinstalled now. It’s not because of its instability, the system still runs and can continue to run well, but my primary workstation gets upgraded to an incompatible hardware architecture (64-bit system). So I can’t simply copy my operating system from the old hard drive to the new one as I used to do on all the former hardware (disk) upgrades.