That's pretty good, I'm jealous! The last time I reinstalled my OS (Slackware) from scratch was 2009, but I run into serious problems every couple of years when upgrading it to 'Slackware64-current' pre-release, because Slackware's package manager doesn't track dependencies and you can just install stuff in the wrong order: I usually don't upgrade the whole OS at once... just have to fix any .so link errors (I've got a script to pull old libraries from btrfs snapshots). I've even ended up without a working libc more than once! When you can't run any program it sure is useful that you can upgrade everything aside from the kernel without rebooting!