People are always talking about how long they've had a particular Debian installation, some upgrading the same box through many subsequent releases.
On the desktop anyway, restless, tinkerish people such as myself have a habit of blowing out their OSes for one reason or another -- usually extensive modification/experimentation that breaks things. Others can't go more than a month without either distro-hopping to the next new release.
Since Linux distributions and BSD project releases and the thousands of software packages that are available in affiliated repositories don't cost anything, there's no incentive to hold onto an installation for years and years like with Microsoft Windows or Mac OS.
I think those with proprietary OSes hold onto their installations more to preserve their stash of pirated applications than the system software itself, which usually can be reinstalled easily from the discs that came with the computer. But that's another matter for another day.
In my case, the reasons for keeping this particular Debian laptop running uninterrupted include maintaining productivity (which I want) and not messing with stability (which Debian Stable has) coupled with my current lack of taste for distro-hopping and repeating the work involved in setting up things the way I like them.
I've been careful with this particular Debian Squeeze installation on my Lenovo G555 laptop, and it's been running pretty much every day since late November 2010. And it's now April 2012.
That's a long, long time for me. I thought I "broke" the system today during some OwnCloud client testing, but it turns out I just clicked something I don't normally click in Gthumb, making it impossible to shrink images while preserving their aspect ratio.
But I figured out what went wrong, Gthumb is working again, and this Debian Squeeze install continues to run.