While the same can not be said for Windows based system, due to the extremely large cross section of hardware and idiots, I haven’t seen a blue-screen since about 2005 either and that is across XP, Vista and 7.
I saw one just the other day at work on my workstation. I wasn't doing anything, just left it on overnight as is policy (for AV updates, system updates, system scans, etc.) and it was BSOD in the morning.
The last time I rebooted my Mac was the last big system update. Otherwise I never even log off, just lock the screen, and I have five people using this system on different accounts (wife + kids). Right now I have four accounts logged on. It stays like that for months, and that never slows it down.